Why does the pen tool work so poorly when editing selected paths. Sometimes it works as intended but often it creates weird inverted paths that no sane human would have guessed was the intention.
It often takes me four or five attempts to make Illustrator understand how I want the path to be edited.
Do I do anything wrong or is Illustrator just really bad at this?
I know that I can erase paths and draw new ones and use Pathfinder to add or subtract but it takes a lot longer to do it like that.
I have no idea from those screenshots what steps you are taking or what result you intend, so I'm siding with the pen tool here.
Maybe the video shows it better.
Basically when having a medium sized path that mostly looks ok, but some part of it is wrong, I select the path and tries to edit it with the pen tool (beacuse it is quicker and I need to do hundreds of these edits).
It works fine sometimes, but very often it creates parallel/overlapping paths, or crops the artwork to the path I edited.
I try to do short edits, long edits, draw clockwise or counterclockwise but can't really see any pattern to when it understands my intention ( shanging part of a path as I intend) Vs creating a random tangle.
That's the Pencil tool, not the Pen.
I can't replicate this problem here. What Illustrator version/OS are you using?
Can you show the appearance/layers panels for the shape you are trying to edit? Or better yet share a demo file?
Probably because you are using the pencil tool, which does different things than the pen tool - you can draw with it, but with the pencil tool you can also edit small sections of a stroke on the fly just by drawing over the line, but as you are finding it can be tricky if you leave an end open. Search for the adobe help on using the pencil tool.