A single bad habit will mar an otherwise faultless character, as an ink drop soileth the pure white page.

One standing fault does disproportionate damage to a reputation built carefully everywhere else. It is not fair, but it is how attention works: the eye goes to the mark, not to the clean space around it. The habit you have decided is minor, the temper, the lateness, the sharp remark, is often the one thing people can name about you.

Pick the fault you have quietly agreed to keep, and stop defending it for one week. You do not need to reform your whole character; just take the single thing that undercuts the rest and work on it while the rest holds.