There is a difference between establishing a deadline and estimating relative effort and complexity. The former is problematic. The latter is important and shou

There is a difference between establishing a deadline and estimating relative effort and complexity. The former is problematic. The latter is important and should be done and then revised continuously. The process of building software includes discussing what has the best impact to effort ratio. Both are estimates and will not come out as expected. The logical response to managers that expect you to always hit deadlines is to inflate estimates enough that you will.