The thing about most RPGs is that many characters are only as good as their equipment. Sure, the extra stats/skills/whatever you get from levelling up is pretty nice, but nothing feels better than finding a +3 sword of awesome at the end of a dungeon.
Likewise, nothing feels worse than losing that same sword because of rolling low once or twice. If you must play with fumbles, hurt the characters; nothing absurd, like chopping all of their limbs off, but going into town and getting healed/getting a replacement arm is far easier than replacing your favourite piece of loot.
Now, that's not to say every piece of loot should stay until your players let it go - stealing something from the players can motivate them quite effectively* - but the differences lie in both the frequency with which it happened (your players should be able to say "Hey, remember that time X lost his favourite toy and we had to get it back?", and everyone should be able to clearly recall the incident>), and the ability to get it back, preferably with a nice little bonus at the end for their trouble.

*Note: Some players get very attached to their gear. In this case, it'll be far more likely to get them mad at you, which is a very different scenario from their characters being mad at the thief. Exercise caution when using this technique.