One of the lakes I fish commonly during the summer will fog over something bad. My boat's 15' length and there are times when I can't see the bow (no, really). Navigating can be tough. I mean I "think" I know the lake but there have been times when I've been running along (at idle or just above) and found myself inches away from the bank, or rocks. It's easier than you think to do it.
Compass? Yep I carry one. Cheap magnetic, but it works. There's a few things I carry, just in case. Not a lot and it don't take up much space but yes a compass is one of them. Multi-tool, etc. Lost the pickup tube off of my portable fuel tank in the middle of the river once. With a multi-tool and McGyvering, I had it going in 10 minutes. Pulled cowling off, removed a clamp from a water hose, clamped the tube in the tank back on and screwd the pickup assembly back down. Motor leaked a little water but it at least ran.
The phone has a decent GPS built into it. Problem is, the phone is electronic. Electronics fail more often than magnetic compasses do. And yeah my phone has failed me once.
Similarly, pilots carrying paper sectional maps. They can't always depend on GPS (if they have it).