That's only if the challenge is completely new. Sure, if you're researching something novel in an area you've not worked on, the information you have is likely very far from complete. But if you're writing a backend server for a new POC for the umpteenth time in your career, you're likely to be able to do it fast, well, and be able to estimate how long it's gonna take. The reason being that the unknowns are slim to none.