Commitment to the shot, or lack thereof, ultimately cost Jordan Spieth a second consecutive Master's championship. Standing over his tee shot on the infamous hole #12, things sped up for Spieth, who admitted he started rushing through his routines and did not fully commit to the shot in front of him. After 63 holes, Spieth had few lapses in his performance, and when he did have a misstep he battled back each time. But bogey, bogey put him on #12 on the final day with a one shot lead, after previously holding a 5 shot lead with 9 to play. Pressure. History. Overthinking. In 2014, Spieth had a similar outcome on hole #12; he found the water hazard then too, which cost him the championship as well. His personal history with the hole created doubt in his mind, which in turn led to carding an unprecedented 7 on a par 3.
Committing to the shot is one of the most important aspects of playing tennis at a high level. Approaching the ball with a clear idea of what to do, followed by fully committing to the decision, leads to better execution and confidence in one's abilities. I venture a guess that if Spieth had committed to the shot in his mind he may still have put the ball in the water; however, the key difference is what would have gone through his mind afterward. If he had committed to the shot and missed he could still move forward knowing that he made the right decision, but just didn't execute (he at least got one of the two right). Instead, he didn't execute BECAUSE he didn't commit to the shot. When you hear a player say "I got tight", this is what they are experiencing; overthinking that leads to doubt, which leads to poor decision making, which leads to poor execution. As one of the commentators stated, "At this point in the tournament, poor play is usually a result of poor decision making." In Spieth's situation, it led to him rushing through his routines and approaching the ball before he was ready to play.
I would imagine that the sleepless nights ahead of Spieth are not because he missed out on an opportunity to win back-to-back Master's, but rather that he didn't commit to his game in the most challenging spot on the golf course. If he had, and even if he still came up short, I bet he would sleep much easier.