Picture the scene. You are a senior figure at an organisation that's messed up. There is no hard evidence that you are responsible for what has gone wrong, so you hope to evade personal blame. So what do you say? You say: "I am very sorry that these problems, of which I was sadly unaware, happened on my watch, and I therefore wish to take ultimate responsibility and resign." Is there a more annoying expression than "on my watch"? It is a way of saying: "I don't want to admit that that this is all my fault, but I have no choice but to resign before I am sacked or arrested, so I shall attempt to appear noble by resigning quickly while it looks like I still have a choice." Funny, isn't it, that it's only bad news that happens "on my watch"? When the team wins, nobody says: "I can claim no credit for this success. Yes, it happened on my watch, so I am ultimately responsible, but, actually, I knew nothing about it."