According to statistics from The Puck Report, only 28 teams out of 290 have clawed their way back from a 3-1 series deficit and won the series. Just under 10% of teams have accomplished this feat. In recent memory, both the Capitals and Penguins have been on the losing side of these incredible comebacks.
2016 was a very weird year. It saw the Golden State Warriors, Oklahoma City Thunder and Cleveland Indians each blow a 3-1 lead in the postseason. Extending into 2017, the Atlanta Falcons did the equivalent, blowing a 20+ point lead in the Super Bowl.