I don't think the point of lowercased's comment was that devs don't underestimate tasks to the same degree that "outside-of-technical-people" might. They are saying that "outside-of-technical-people" don't have the experience to understand how difficult it is to give an accurate estimate or how much pressure is put on devs to agree to a deadline and take responsibility for making something happen by that date. This is compounded by the fact that stakeholders are unwilling to define or commit to a detailed set of features or acceptance criteria. The bigger the project, the more painful and difficult this becomes. Stakeholders say "Make it faster!!!" then engineers say "We agree!!! any ideas on how?".