A clean apology settles in two minutes what a defensive one drags out for weeks. It needs no gift and no speech, only ten minutes alone beforehand to think it through, a quiet moment face to face and the discipline to leave out one word: ‘but’. It works the same for a partner, a friend or a colleague.
name exactly what you did
Write down, in one sentence, what you did and what it cost the other person. Be specific: ‘I lost the book you lent me and let you ask for it twice’, not ‘sorry if there was a misunderstanding’. Leave out ‘if’, ‘maybe’ and ‘mistakes were made’. A precise sentence shows you understand; a vague one leaves them to do the explaining.

say sorry and then stop
Sit facing them, phone out of sight and say it within a day: the sentence you wrote, then ‘I’m sorry’. Stop there. No ‘but’, no reasons, no account of your week. An explanation straight after an apology sounds like a defence. If they ask why, answer in one sentence and leave it. Let the silence last; ten seconds is fine.

offer one concrete repair
Offer one thing you will do, not a promise to be better: ‘I’ve ordered a new copy; it arrives on Thursday’. Make it something you can finish within a week, then finish it. Do not ask whether they forgive you; that hands them a second task. Let the repair speak and drop the subject once it is done.

The common mistake is the word ‘but’: it cancels everything said before it and it is the part they will remember.