No reproof or denunciation is so potent as the silent influence of a good example.

Being told you are wrong puts you on the defensive; watching someone quietly do the thing better leaves you nowhere to argue. Criticism gives the other person something to push against, and most people would rather win the argument than change. An example offers no opposition at all, which is why it works slowly and then completely.

Think of the person whose conduct you keep meaning to correct. Instead of the conversation you have rehearsed, do the thing correctly yourself, in front of them, without commentary, for a few weeks, and see what shifts.