I think there's two kinds of situation this occurs in. There's the "not yet learnt" kind where people don't know what they can deliver, over-promise, and end up

I think there's two kinds of situation this occurs in. There's the "not yet learnt" kind where people don't know what they can deliver, over-promise, and end up in an awkward situation. There's also a trickier, structural situation that I think is more common. If managers don't have real ownership of their client relationships, they learn they become effectively unable to say "no". If they try, someone else will say "yes" instead.