Write the goal in pen. Pencil makes it way too easy to quietly erase once things get hard.

Commitments that can be revised without anyone noticing tend to shrink exactly when they get difficult. Making a goal permanent and visible removes the quiet exit, so the only options left are doing it or openly deciding not to. Both of those are honest, and the slow erasing is not.

Put the goal somewhere it cannot be edited privately: told to a friend, written on the wall, dated on paper. If you later change it, change it out loud and say why. Watch this week for the moment you feel the urge to soften the wording.