One thing that I get sick of is how people take an estimate, expect it to be accurate, feed it into a plan, and when the plan is (inevitably) proven wrong, blame the estimate. This is a fallacy from the era of Waterfall development, but it still lingers on in many Agile environments. ... Consider this: in Australia, it's usual for every person to get 4 weeks of leave per year (which, on average, they take all of it eventually).Surprise! People take vacations!
Expecting an estimate made several months earlier to be accurate is crazy - but people still do it.
Software is too expensive to build cheaply...: Estimation vs planning