"I found a rock that can stick to metal." Would instantly conjure up several hundred ideas of how to use it. "I found another rock like it, and they magically push against each other if you hold them one way, and pull on each other if you hold them the other" would create about a thousand more. Only thing you need to know to fund magnets useful is what a magnet is, and if you know enough to say "magnets are useless", you know what magnets are