The thing to keep in mind most of all is that it's an exercise. Exercises are where we make mistakes, where we struggle against things at the edge of our ability or beyond it, and where we grow by way of that struggle. So the fact that it's so challenging isn't something we necessary should be avoiding.

But it is very challenging, because of how compared to other textures that are much more regular (like the wax example) don't end up with large chunks of surfaces that are at dramatically different angles than if we were just dealing with a simple flat one. Yeah, there's curvature and deformation, but compared to having a scattering of box forms that can be set at any old angle, it's day and night.

The thing to avoid in terms of what results in form shading is that you have to remember that every shadow you add is a new shape. It can be tempting to fill in existing shapes (like the side planes of your lego blocks), but that is precisely what form shading is - the entirety of a surface getting darker or lighter based on its relationship with the light source.

A cast shadow will fall upon one of these surfaces, but it more often than not is only going to cover part of it - and even if the whole thing gets engulfed, the process of first designing that shadow shape by outlining it will help you avoid situations where you just automatically fill in those existing planes.