A respected colleague makes a serious mistake that could create a major problem for the company. Reporting it immediately may badly damage their career, but giving them time to fix it quietly could expose you to risk. What would you do?

Report it immediately. Respect for a colleague cannot outweigh the risk of a major company problem. If I stay silent and things deteriorate, I have made myself part of the concealment. They can explain the mistake and any corrective action through the proper process.

I would give them one very short, clearly defined opportunity to start fixing it, while making it plain that escalation will follow if the risk remains. Quiet correction should not mean indefinite secrecy. The seriousness of the possible damage sets the deadline, not personal loyalty.

A private warning sounds compassionate, but it also transfers responsibility onto the person who noticed the mistake. I would lean toward reporting it, perhaps after telling the colleague what I am about to do. Transparency is fairer than making a secret arrangement neither person may be able to control.

I would let them try to fix it first. A respected colleague should not have a career badly damaged without even being given a chance to put matters right. But that chance must be brief and honest; if they minimize the problem or fail to act, reporting becomes unavoidable.