I'm with White Knight on this one.
This was not about navigating around CB's or flying a difficult approach.
A simple mistake was made during calculation of T.O. data (ok, can happen) but because of cutting corners the error did not get picked up at a later stage. You should know when to cut corners and when not. And if you intentionally remove the safety net during TO calculations...it means you have NO idea what you are doing and you are playing with the lives of hundreds of people behind you....
It's called complacency. Simple.