Even for experienced people, being off by a factor of 2 or 3 appears to fairly normal. That means, the correct answer to "How will this not happen again?" is to

Even for experienced people, being off by a factor of 2 or 3 appears to fairly normal. That means, the correct answer to "How will this not happen again?" is to say that it will happen again, and that that isn't preventable. At least, no one seems to have succeeded at preventing it. My experience has been that the only questions management should bother with are usually the issues that managers can actually fix. That tends to be a surprisingly limited set of things.