By apologizing you open up all sorts of doubts about your competence, your intentions, any other mistakes you may not have confessed. Excuses satisfy no one and apologies make everyone uncomfortable. The mistake does not vanish with an apology; it deepens and festers. Better to cut it off instantly, distract attention from yourself, and focus attention on a convenient scapegoat before people have time to ponder your responsibility or your possible incompetence.
