Picture frames.

Looks like an incredibly simple project for a beginner woodworker, doesn't it? Get some nice wood, rout in a rabbet for the glass/art/backing, rout on a nice decorative profile, then set your miter saw to 45 degrees and make 8 miter cuts, apply some carpenter's glue then wrap it in a band clamp. What's so tough?

I'll tell you what's tough: the precision with which those miter cuts must be made is exceptionally fussy. Say each cut is a quarter degree off. Well, after eight cuts that's two degrees of error. Three of the joints will look fine, the last one will look like an axe wound.

The issue isn't making the cuts at 45°, it's making them at 45.0000°. Or, more realistically, making them truly complementary.

This same issue applies to moldings around cabinetry, with the added bonus that the carcass of the cabinet won't let any of the joints close tightly, so they all look like trash.