They're actually not so hard as you'd think. If you can draw two lines the same distance apart, and find a good reference, you're most of the way there. After that, it's all patience. And if you can forget that your hand hates you, they're actually very good for meditation. Like friendship bracelets. xD
Nah, I'm just kidding. You're still waaaaay braver than me. I've never even tried Celtic knots before.