[perlgeek]

It's not that easy.

If a team member gets sick for a week, it can already be impossible to meet the goals of a two-week sprint.

It happens (not so often, but it does) that we underestimate the complexity of a task by a factor 5 or so; that alone can also make it impossible to meet the goals.

There are just too many things that lead to building pressure when there's no actual need for pressure from a business point of view.

[darkerside]

Estimation is just educated guessing. If you were guessing a non-randomly generated number, and you found you were guessing high every single time, wouldn't you eventually try reducing by orders of magnitude?

Team members do get sick, scope tends to sprawl, and life just generally gets in the way; but good estimation includes a buffer. Under-promise and over-deliver, at least until you figure out what you're doing.