To find a similar case that describes the relationship between head coach Rick Carlisle and the Dallas Mavericks, let's go back to the wonderful days of high school.
You're in a good relationship with a girl you really like. Everything is going great, the dates are fun, the times are exciting, you enjoy the person's company, and life is good.
Then one day, after months of what appears to be a successful relationship, you find out from one of your best friends that your girlfriend hooked up with your ex-girlfriend's older brother's cousin—or something ridiculous like that.
All she did was hook up with one guy—nothing drastic like plowing through the whole high school football team behind your back and then announcing it over the PA system before school. Nope, just a single one night stand.
However, that causes a slight tear in the relationship that was at one point seamless.
What used to be taken for granted as reliable and trustworthy now has suffered a crack, albeit the tiniest of slip-ups. Once that crack has been made, you could continue on with that person, but there's always the thought in the back of your mind: "It might happen again."
Pretty soon, the crack caused by that one event leads to a full out break. Game over.
That feeling caused by the tiny tear in the relationship is how I felt after the Mavericks' season came to an unceremonious end to the Spurs.
For the most part, everything had been going well this season: The Mavs went 55-27 and had a league-best 13 game win streak at one point. They got the two seed in the playoffs, which translated into home court until the West Finals. Dirk and Co. rode a five game winning streak into the series against the Spurs and even took Game One in business-like fashion.
Then Carlisle cheated on us. He slipped up.
After that series, I simply cannot trust Rick Carlisle anymore.
What seemed to be a healthy relationship has been damaged and that damage, I believe, is irreparable. I'm never for firing a coach immediately after a big loss, but Carlisle's management of the team over those two weeks was so egregious I will make an exception.
Now, if we want to stick with the high school methaphor, Carlisle did not hook up with someone to make every Mavs fan jealous. He simply got drunk at a party (in this case the playoffs), saw a cute girl that wasn't his woman (in this case looking at the wrong lineups), then forgot about his lady (in this case, the right players who would deliver).
Just like in high school, there were subtle hints that something bad could potentially happen. It wasn't enough to raise a whole lot of concern during the regular season (the majority of time spent together) but, once we got to the postseason (the party), those hints translated into a full out disaster.
Carlisle messed up and that mistake is enough for the Mavs to break up with him.
Now on to the reasons.