Habits
Think only about the next round
In one line: The last round is over: take with you only what you learned.
Why
Going over a mistake while playing the next round takes your attention just when you need it. A mistake remembered well is a lesson; one you keep reliving becomes a second mistake.
How to train it
After every lost round, tell yourself one sentence about what you will change, then let it go. In the buy phase think only about the plan.