People, especially customers, forget the real definition of an estimate. Its an estimate. Not a guarantee. But because they forget this they are generally unhappy if a delivery is going to be ‘late’. And with lateness comes blame. And, good guys don’t get blamed. Its the arses fault.
Good guys get out of this blame problem by getting good at the ancient art of Schedule Chicken. In every delivery, there is almost always a set of dependant deliverables. To win the game all you have to do is bet that one of the other deliverables will deliver late and, crucially, declare they are going to be late before you have to. Therefore, you gain the extra time their slippage offers.
So, the easiest way to for you to get some slip in your project is to let someone else do it for you and, presumably, take the blame.
Schedule Chicken should be played with caution and definitely not by an arse. Watching an arse attempt to do it is however, very funny. This is particularly good when an arse is playing schedule chicken against you and you know you are going to deliver on time. Supply misinformation that suggests to him, off the record, that you might be a bit late. He’ll rub his hands together in glee hoping that you have given him a way out of his own slippage. This joy will be short lived as he finally declares that he is unable to deliver one day before the project is due and is ripped a new one.