The approach recommended in the talk is to use relative size estimates instead of absolute size estimates, which removes the possibility of over-estimating (or

The approach recommended in the talk is to use relative size estimates instead of absolute size estimates, which removes the possibility of over-estimating (or under-estimating) or sandbagging. During the conversion phase from relative sizes to absolute sizes (which should be based on historical measurements, not aspirations), you can choose to add a bit of extra time so that people can work carefully and fix things rather than feel rushed. That's often a very good idea.