I 90% agree with Josh, that rope snapping in the knot isn't a likely failure scenario unless many other things are already catastrophically wrong in which case the knot wasn't your problem. So the strength of common knots isn't often very relevant.
That all said.. I been wrong and surprised by counterintuitive stuff. For example joining two ropes by just trying a fig 8 in the two ends (not sure I'd have done that rather than a double fisherman's or a rethreaded 8?) is dangerous and can roll undone, whereas the scary looking overhand "European Death Knot" / "EDK" (
https://en.m.wikipedia.org/wiki/Offset_overhand_bend) is far safer and much less likely to get snagged on rock when retrieving. Now I'd never have expected that
Or.. when using dyneema/spectra/etc materials for cords, a double fisherman's knot is absolutely unsafe (can slide and roll undone at amazingly low loads, like 1kn in some cases) whereas for a normal rope or cord it's an ideal choice
So a bit of education can be useful on knots (thanks MikeM) but I'm not earning some scout badge or something to be a knot nerd to memorise percentages, but sometimes there are unintuitive things and we can all benefit from learning