Finding any semblance of rhythm or consistency within the realm of the UFC can prove an arduous task. Every time a contender moves a step up the ladder, that fighter must immediately prepare to up the ante in terms of their level of competition.
In rare cases, top-tier fighters like Anderson Silva, Jon Jones and Georges St-Pierre perpetually evolve in order to rise to the occasion and meet their obstacles.
But not all of the UFC's 376 signed fighters can lock horns with the world's best scrappers bout after bout and maintain their job security.
Each of the 10 fighters who landed on this list have routinely experienced euphoric highs and demoralizing lows, sometimes in immediate succession.
Here's a glimpse at the 10 most inconsistent fighters in the UFC.
1. Rousimar Palhares
2. Brian Stann
3. Joe Lauzon
4. Jamie Varner
5. Rich Franklin
6. Frank Mir
7. Tim Boetsch
8. Brendan Schaub
9. Josh Koscheck
10. Manny Gamburyan
Few experts would have dared to place the 34-year-old Penn on a list like this back in 2009, particularly after watching the Hawaiian savagely dismantle Diego Sanchez at UFC 107.
His victory over Sanchez gave "The Prodigy" a UFC record of 11-4-1, including a mark of 10-1-1 in lightweight tilts.
But in the six bouts following Penn's win over Sanchez, the former two-division champ went 1-4-1, with his only win in that span coming against a fading Matt Hughes.
Penn has never blamed his decline on the aging process, but The Prodigy turned 31 the day after crushing Sanchez, and since then, he's tasted victory just once.
Some fighters, like Silva, seem to have the fountain of youth at their disposal. Others, such as Penn, seem to lose a step every time they compete.
Once considered one of the top pound-for-pound fighters in the world, the 31-year-old Mauricio Rua has essentially been a model of inconsistency since joining the UFC in 2007.
After a brilliant career in Japan's Pride Fighting Championships, in which he won 12 of 13 fights, "Shogun" flopped in his greatly anticipated UFC debut against Forrest Griffin.
Following his loss via rear-naked choke to Griffin at UFC 76, Rua rebounded, winning three of his next four tilts, including an impressive knockout of Lyoto Machida in their rematch for the light heavyweight belt at UFC 113.
But in his five scraps after capturing the strap, Rua failed three straight litmus tests against the division's best.
Rua first lost his belt when he got shellacked by Jon Jones at UFC 128.
The Brazilian then avenged his loss to Griffin with a vicious knockout at UFC 134.
But just when it appeared Rua could get back into title contention, Shogun went 1-2 in his next three fights, dropping decisions to both Dan Henderson and Alexander Gustafsson and finishing the struggling Brandon Vera.
With a 5-5 record in the UFC, Shogun could have easily landed higher on this list. However, because he's only taken on upper-echelon opponents, he narrowly made the cut.
Indicative of his inconsistent ways, Dan Miller reeled off three consecutive wins (two by submission) when he joined the UFC, and then dropped his next three bouts (all by unanimous decision).
Miller certainly looked like a contender in the middleweight division when he guillotined Jake Rosholt to tally his third straight win in the promotion at UFC Fight Night 17.
However, once pitted against top 10 contenders, Miller froze, suffering three consecutive losses to Chael Sonnen, Demian Maia and Michael Bisping.
Miller regrouped and strung together a two-fight winning streak with victories over journeymen John Salter and Joe Doerksen in 2010. But Miller again diminished his winning streak with a two-fight losing streak, this time dropping consecutive unanimous decisions to Nate Marquardt and Palhares.
The 31-year-old Miller sports a 6-5 record in the UFC and has easily handled every unranked opponent he's faced in the promotion. It's his negative encounters with perennial contenders that landed him on this list.
Paulo Thiago's first two fights in the UFC's welterweight division marked the onslaught of an inconsistent career with the promotion.
A significant underdog, Thiago KO'd Koscheck with a flush uppercut-left hook combination and garnered a "Fight of the Night" bonus in his promotional debut at UFC 95.
Less than five months later, at UFC 100, Thiago got outstruck 127-13 and surrendered four takedowns in a unanimous decision loss to former title challenger Jon Fitch.
Since losing to Fitch, Thiago has struggled to find any rhythm, going 3-4 and suffering his first loss by knockout to Siyar Bahadurzada.
Thiago's ability to finish dangerous opponents like Koscheck and Mike Swick once made him a top 10 welterweight. His inability to outlast the division's studs has landed Thiago on this list.
Already both a legend and a model of consistency before joining the promotion, Antonio Rodrigo Nogueira has only experienced checkered success in the UFC's heavyweight division.
In just his second fight with the organization, the 36-year-old "Minotauro" guillotined Tim Sylvia at UFC 81 and took home the UFC's interim heavyweight belt.
In his ensuing bout, however, Nogueira got roughed up and eventually finished by Mir, giving up his interim belt at UFC 92.
"Big Nog" followed up his loss to Mir by going 3-2, earning wins over Randy Couture (unanimous decision), Brendan Schaub (KO) and Dave Herman (armbar), but getting finished by Cain Velasquez (KO) and Mir (kimura).
Expected to coach opposite Fabricio Werdum on the second season of The Ultimate Fighter: Brazil, Nogueira will try to best "Vai Cavalo" for the second time in his career. If he does, Minotauro will start just his first winning streak in over five years.
Like the five fighters before him on this list, Roy Nelson has dispatched better-than-average opponents, but has perpetually looked like the inferior man against top-flight competition.
After first knocking out Schaub at The Ultimate Fighter 10 Finale and then finishing Stefan Struve in similar fashion at UFC Fight Night 21, "Big Country" squandered a big opportunity to move up the ladder with back-to-back unanimous-decision losses to Junior dos Santos and Mir at UFC 117 and UFC 130.
Granted, Nelson has won three of his last four fights, including a first-round TKO of Matt Mitrione in his last outing at The Ultimate Fighter 16 Finale. But in the most pivotal of his last four bouts, Big Country fell convincingly to Werdum in a unanimous decision loss at UFC 143.
Werdum outstruck Nelson 98-55, including 91-26 in the "significant strikes" category.
Nelson will once again get a crack at moving closer to title contention when he tangles with another inconsistent fighter, Cheick Kongo, at UFC 159. With a win, Big Country can also start to shed his label of divisional gatekeeper that Kongo already reluctantly carries.
Pat Barry knows how to win in the UFC. He's done it five times since 2008.
What Barry can't figure out, however, is how to start a winning streak. In 10 fights with the promotion, Barry has tasted victory five times and defeat just as many. The only streak he started in that span was dropping back-to-back fights to Kongo and Struve.
It seems like the only thing UFC president Dana White can rely on Barry for is finishing fights and getting finished. HD has prevailed four times by form of knockout and once by decision, and has lost three times by submission and twice via form of knockout.
Most of the 33-year-old Barry's dependability issues stem from his lack of grappling dexterity. If Barry can't shore up his grappling deficiencies soon, he may never start a winning streak in the UFC.
Only two current fighters, Penn and Koscheck, can say they've graced the UFC's Octagon more times than Chris Leben, who's fought 20 times in the promotion.
Although he clearly possessed the talent to rack up 12 wins in that span, "The Crippler" has always found a way to keep his name out of title contention.
In a way, Leben has sabotaged his career by refusing to evolve his one-dimensional game and by leading such a volatile and reckless personal life.
The Crippler's chaotic fighting style may have produced plenty of highlight-reel knockouts, but that same flair has cost Leben several knockout and submission losses.
The Crippler twice smudged his persona outside the Octagon, testing positive for stanozolol after a loss at UFC 89 and testing positive for oxycontin following a setback at UFC 138.
Leben, who's lost three of his last four bouts, has gone on notable winning streaks before in the UFC. But that was long ago and the game has changed radically since then.
For Leben to ever generate another winning streak, he'll need to make some substantial changes.
Any fighter who can follow up a four-fight winning streak with a four-fight losing skid, which is precisely what Dan Hardy did in his first eight scraps in the UFC, deserves a slot at the top of this list.
Like many of his unreliable peers, "The Outlaw's" inability to adjust to higher levels of competition have sent him into tailspins at times. But when pitted against the welterweight division's bottom dwellers, Hardy has flourished greatly.
The Outlaw scored four straight wins over Akihiro Gono, Rory Markham, Marcus Davis and Mike Swick between October 2008 and November 2009. Hardy then stumbled miserably against St-Pierre, Carlos Condit, Anthony Johnson and Chris Lytle between March 2010 and August 2011.
Known for his smooth and technical striking, Hardy has since rebounded with back-to-back wins over Duane Ludwig and Amir Sadollah. But akin to Leben and Barry, Hardy won't ever graduate from gatekeeper status until he vastly sharpens his ground game.
Consistency wasn't an issue for Wanderlei Silva until the tail end of his highly fruitful Pride career.
That's when Dan Henderson and Mirko Filipovic each rendered Silva unconscious in back-to-back bouts, dropping the violent Brazilian in the same manner that he had flattened so many unfortunate foes in the Japan-based organization.
Shortly thereafter, "The Axe Murderer" started his UFC career on the wrong note, getting outshined by Chuck Liddell in a memorable unanimous-decision loss at UFC 79 to suffer his third straight setback.
Getting KO'd by both Henderson and Filipovic and duking it out with Liddell apparently weakened The Axe Murderer's chin considerably.
Wear and tear, however, hasn't stripped Silva of his knack for landing knockout blows. Following his loss to Liddell, Silva went 4-4, but scored a KO of Keith Jardine, a TKO of Cung Le and a KO of Stann along the way.
Silva may never sniff a title shot again, but the Axe Murderer will always have blessings from both White and the fans for the same reasons that guys like Barry, Leben and Hardy do. Finishes in the UFC are exhilarating, regardless of who the victim is.