Getting into an "unsolvable" state is a major painpoint in FreeCAD (and in many other parametric modellers). However you rarely, if ever, need to do everything

Getting into an "unsolvable" state is a major painpoint in FreeCAD (and in many other parametric modellers). However you rarely, if ever, need to do everything again. There is usually a way to rebase your features to solve the issue. But how to achieve this requires strong conceptual understanding, and knowledge of some FreeCAD quirks. Map Sketch to Face is a key tool, and knowing that one has to show/select the correct version of the object. For really tricky cases the DAG graphviz visualizer can be useful. Also there are certain design patterns that are less vulnerable to catastrophic model failures. Smart choices of booleans versus feature operations and ordering of these are key to a "robust" design. Having waded through this process quite some times. I should really do a video tutorial on the subject...