The author suggests that project estimations are frequently biased by optimism and pessimism. He argues that optimism on estimates usually appear when a lack of experience leads us to ignore unknowns and underestimate tasks. On the contrary, negative previous experiences drive us to overestimate schedules. Given what you read, as well as your own experiences, in your opinion, what is worse: over or underestimating? Is there a way to combat the tendency to do these things based on our past, negative experiences or our need to be optimistic about the outcome?