My Advice to You, the New Quitter:
Live your life in “day-tight” compartments.
In other words, treat every day as its own separate thing:
Don’t waste time and energy regretting what you did (or didn’t do) yesterday (or the day before that, or the day before that…); the past is over, it’s carved in stone, you can’t take it back, and you can’t change it.
Get over it.
And don’t waste time and energy worrying about what might happen tomorrow (or the day after tomorrow, or the day after that…); you can’t do anything about tomorrow until it becomes today.