This is often the advice given by senior folks and I think it is somewhat similar to say that you have to "lie a bit on your CV". Still, I always wonder what would I do if I make these big promises to clients/bosses/management and I fail to deliver. Wouldn't that be worse than having said "no, I won't be able to make it in time" from the beginning?
For context, I'm early in my career (3 YOE) and I don't deal with management that much yet (I'm still shielded by my tech lead and PM), so I'm always looking for advice on how to navigate these things. I really can't just say "YES, YES, YES" when I know *very well* that something won't be possible.
Maybe it is just a sign of being too junior?