Flexbox is a gnarly complex piece of CSS but it needn’t be too hard to come to grips with. Opera’s Bruce Lawson explains how to best understand flexbox via an analogy.
As a quick tip, I find a helpful way of coming to grips with it is by likening Flexbox to String Theory. Thus, flex-basis is analogous to a Calabi–Yau manifold, and think of flex-shrink as like the 7 compactified dimensions propagating from one point to another by summing probability amplitudes.