My friend Holly Whitaker, author of Quit Like a Woman: The Radical Choice to Not Drink in a Culture Obsessed with Alcohol, has helped make the saying "Never question the decision" popular in the recovery community. She has written and spoken about it as meaning "Never question the decision to get sober or to recover—once you have made that decision, just go with it." I get where she is coming from, and I think she's brilliant.
The thing about recovery, especially if it's recovery from substance issues, is you can spend an awful lot of time in your head asking yourself, Was it really that bad? Can I really never do that again?
What if I just did this or what if I just did that? What if I only had one?
It's a lot easier to leave those thoughts alone, to just remind yourself you've made the decision that you aren't going to drink, smoke pot, gamble, overwork, or call up that person who doesn't deserve you. Treat your decision as a given, don't give it space or energy, shut down those questioning thoughts as they arise.
Keep your commitment to yourself. There was a reason you made the decision in the first place.