[gilbetron]

"we have never missed an estimate"

After 35+ years of software development, you are either lying, incompetent, or worked on exceedingly trivial software. Sorry to be harsh, but I can guarantee you that if you were given a significant software project, asked to estimate and then deliver, that the vast majority of the time your estimates would be wrong.

[JohnFen]

They could also be greatly padding their estimates. When I estimate things, I take the amount of time I think it will require and double it. In my businesses, my partner would take my padded estimate and quadruple it. By doing that, we never blew past a deadline promised to a customer. That doesn't mean the estimates were accurate -- if they were, no padding would be necessary.