The classic failure is not the hole. It is the patch. You fill it, it looks level, it dries, and now there is a slightly sunken circle catching a shadow in exactly the spot you were trying to make invisible. Paint over it and the shadow is still there, just the same colour as the wall.

Filler shrinks as it cures because the water in it leaves. A blob pressed into a hole is thickest in the middle, so the middle loses the most volume and pulls down. That is the dish. It is not a mistake in your technique; it is what happens when you put too much material in at once.

The scraper is the reason this kit works rather than the paste. A flexible blade drawn across the wall does two things at the same time: it presses filler in and it takes the excess off flush, so what stays behind is only as deep as the hole. Less material, less shrink, no dish.

Which makes the method almost the opposite of what feels right. Do not build it up. One firm pass with the blade at a low angle, then leave it alone. The urge to go back and add more, or to smooth it with a finger, is the urge that creates the work you will be sanding tomorrow.

The limit is size. This is for nail holes, screw holes, small dents and scuffs, up to roughly the width of a coin. A hole big enough to see darkness through has nothing behind it for the filler to key into, and it needs a backing patch first. Filler bridged across an open cavity cracks the first time the door slams.