TFA offers one reason: uncertainty-based rescaling — leads people to systematically overestimate the size of small values and underestimate the size of large v

TFA offers one reason: uncertainty-based rescaling — leads people to systematically overestimate the size of small values and underestimate the size of large values. Basically, when you're not sure what the actual number is, you tend to anchor your guess on 50%, not 0% or 100%.