If history has taught us one thing about the first round of the Stanley Cup Playoffs, it's that nothing is certain.
With multiple games every night unfolding at a fast and furious place, it's virtually guaranteed that we'll see crazy upsets, underachieving superstars and unexpected heroes.
Night 1 of 2014 didn't disappoint with some fast, intense, wide-open hockey from teams that are just getting to know each other. The pre-existing rivalries will get underway later in the week.
Here's a look at each series' unique X-factor, whether it's a person or a situation, that could play a key role in the NHL playoffs.
All stats current through Wednesday April 16, courtesy of NHL.com.