I think the main theme of Field of Dreams is second chances. After we've made a mistake, and life is a parade of mistakes, a second chance is something we yearn for, and yet is so rarely granted. Baseball is the ideal metaphor of the Second Chance. First of all, because there is no clock, a comeback is never impossible. And if you don't come back, there is tomorrow.
Baseball is played every day.
If you don't succeed, you'll have a brawl in the clubhouse and a chance to do it all over again the next day. If this takes away some of the sting of defeat, I suppose it also takes away some of the sweetness of victory. Tomorrow is always another ballgame. And as a game can ebb and flow, with winning moments and losing moments, so can life. The important thing, I guess, is to have more winning moments than losing.