It's for their own good. You know it. Putting them through the absolute worst situations you can imagine not only makes for good story telling, it is often the catalyst for the change necessary for them to grow.
Okay, you agree? Good, except that making mistakes isn't enough. Having bad things happen isn't enough. It's DEALING with it that makes the character and the story rich. You might think you've put your MC in danger, tortured her, etc. When in truth you've sent in a "rescuer" to prevent her from actually suffering. Do any of these sound familiar?
- The love interest swoops in and saves the day. Enter Edward Cullen - maybe we should deem this the "Edward Interference"? My but the MC had a fright! It's a good thing our mysterious, brooding hero who may or may not be immortal was around to save the day. No! No! No! None of that please. What kind of character arc does your MC have if Mr. Macho is always preventing things form happening?
- It was all a misunderstanding. *shakes head* Life isn't fair. If the MC gets to let it roll off her back and skip through the sunshine and rose petals it won't make for a very good story. Trust me. No coincidences. No "but it really wasn't what she thought so no harm done" situations please!
- Something bad happens, but it's immediately remedied. Okay I hurt her - quick where's the bandage? Tension friends. Let the ramifications sink in. Let 'em wallow in it. Don't stick her in quicksand when there's a strong, handy branch waiting inches away. Where's the character building there? Where's the excitement for the reader? Draw it out.
It all comes down to the same thing. LET THE MC SUFFER.