I just started reading "Permanent Record" by Edward Snowden and to begin the book he claims one of the most important lessons he learned was from the game Super Mario.
In the original Mario games in which they were a 2d side scroller all you could do was move forward. You could never go back to the left. The invisible wall he said, is the perfect parallel to how we live life.
As much as we may want to go back and collect that missed coin or snag another power-up, all we can do to is continue to move forward.
Beating Bowser requires you focus on the task at hand, and don't waste a single second focusing on what can't be changed.