Score yourself on how well you played the hand, not whether you won. While poor outcomes are excusable, sloppy preparation and decision-making are not.
Book: Poor Charlie's Almanack
In their words:
It is the blend of discipline and patience exhibited by true masters of a craft: an uncompromising commitment to “properly playing the hand.”
Like world-class bridge player Richard Zeckhauser, Charlie scores himself not so much on whether he won the hand but rather on how well he played it.
While poor outcomes are excusable in the Munger–Buffett world—given the fact that some outcomes are outside of their control—sloppy preparation and decision-making are never excusable because they are controllable.
While poor outcomes are excusable, sloppy preparation and decision-making are not. Therefore, you must have an uncompromising commitment to “properly playing the hand.”