A primary learning process is research. This process is part of all science, engineering, management processes. Here's a starting point for learning how to estimate in the presence of uncertainty on agile projects.
This is the start of a literature search. Anyone making suggestions about making decisions in the presence uncertainty on agile project can start here for establishing the basis of any arguments of how and why that suggestion (conjecture possibly) is based on some set of principles. Not just anecdotal opinion.