I chose FreeCAD and did the basic part design tutorial. It teaches first things like constraints, extrusion from 2D to 3D, padding/pocketing, linking to external geometries, symmetry, etc.
It was estimated to be “less than an hour” but it took me longer. Here is an animation of me eyeballing the finished part to make sure I didn’t mess it up.
I bet working in CAD regularly changes the way a person looks at the world; how things are built up, cut away, or combined to make their final shape.
Note: the animation was recorded with byzanz and scaled with gifsicle.