If you give an incorrect estimate, you'll be the one to blame at the end of the project. Remember estimates aren't promises, so better to deal with hurt feelings at the start of the project.

The way it usually works is that I say it will take 12 months and the response is "we need it in 6". So I say "fine, we'll give it a go but I am not making any promises" and off we go.

The scope must then be cut, or the project careens into Fantasyland. That happens at some places understood, a sign of incompetent management.

I think the game everybody is playing that it's easier to ask for more money when something is already half done than asking for the whole budget upfront. And you can also cut/adjust scope in the middle.