GIMP makes uncommon things possible, and common things hard. I really don't understand the mental model of people (the devs) who think the GIMP UI is intuitive. It's such a powerful, widely used program, I have always thought it was just me, not understanding some paradigm. But Photoshop is as or more powerful, and yet is so much easier to work with. And it isn't only casuals using Photoshot; professionals do too, so it's not just that GIMP is designed for power users.

I honestly don't understand how the GIMP UI can be so consistently and enduringly difficult.

Draw a straight line with GIMP. I dare you.