I've always thought that typically overoptimistic estimates tend to be more based on the mode. I.e. 'this is the sort of task that normally takes 1 day, so I'll

I've always thought that typically overoptimistic estimates tend to be more based on the mode. I.e. 'this is the sort of task that normally takes 1 day, so I'll estimate 1 day'. The high point on the probability curve is the most noticeable, but it's also way further to the left than either the mean or the median. I have no data to back that up though.