I stuggled with GIMP at first, it was super frustrating because it does UI things differently than other image tools.
i.e. in other tools your active layer masks your drag selection, and in GIMP I would constantly be grabbing lmages from another layer, till I realized the pixel under pointer determines what image is moved. That function can make you highly productive since you don't need to preset layer, but god was it enraging at first