Using an arbitrary Point On Curve to set the height of the shelf instead of a direct measurement of its ‘Z’ value doesn’t make sense to me. The shelf doesn’t need to be a trapezoid but I can’t touch this anymore, sorry.
As to what is obvious or not… That error message was pretty unambiguous to me, and if it wasn’t, I would RTFM before posting a question to the forum.
a term showing the frustration of being bothered with questions so trivial that the asker could have quickly figured out the answer on their own with minimal effort, usually by reading readily-available documents. People who say “RTFM!” might be considered rude, but the true rude ones are the annoying people who take absolutely no self-responibility and expect to have all the answers handed to them personally.
I realize this attitude is considered impolite and disruptive by some (especially in Europe?), but short of ignoring a thread completely, there has to be a more constructive way to respond to questions like this besides patient repetition and hand-holding?