Do you want to know the secret of magic? Then look no further than Harry Potter and the Philosopher’s Stone, page 51, British Hardcover. As everyone’s favorite half-giant introduces Harry to the wizarding world, we’re treated to this intriguing little exchange.

‘But what does a Ministry of Magic do?’

‘Well, their main job is to keep it from the Muggles that there’s still witches an’ wizards up an’ down the country.’

‘Why?’

‘Why? Blimey, Harry, everyone’d be wantin’ magic solutions to their problems. Nah, we’re best left alone.’

What I think Hagrid is trying to say here is that magic, despite its reputation, cannot solve all the world’s problems. It’s a tool to be used, not a replacement for your brain. Despite this warning, I’ve seen more than one mage use a “detect” spell in place of common sense. The classic example is the “can I smite it?” paladin. This guy looks at an NPC, asks, “Is it evil?” and then swings for the fences. Never mind that the poor decapitated schmo was the king’s royal vizier.

Same deal with magic detection and magic items. Doing a quick scan of the room is a good idea, but there are too many lead-lined caskets in the world to make detect magic a good replacement for an old fashioned Perception check. Heck, one of the modules I ran recently threw a ring of regeneration in front of a 7th level party. That thing was worth nearly four times the suggested wealth-by-level for a 7th level PC, and the party sold it for a measly 150 gp because it didn’t have a detectable aura. No one thought to try it on.

Granted, that last one was a bit of a dick move on the module’s part, but the point stands. Assume nothing. Investigate everything. Don’t let magic do your thinking for you.