Your word only means something on the days keeping it is annoying.

Promises are free when they are convenient. Everybody keeps the easy ones, so those tell you nothing about a person, yourself included. The test arrives when you are tired, something better came up, and nobody would really blame you for backing out. What you do in that exact moment is the entire content of your reputation.

Notice the next commitment you want to wriggle out of, and do it anyway, even badly. Or get better at saying no in the first place, which is the honest version. Either way, the aim is that people can plan around your yes.