Meatloaf, pizza, whatever. It tastes better the 2nd day, preferably while still cold from the fridge. And I like neither meatloaf nor pizza when they're fresh.
I don't know why it works this way, but it seems to be a universal truth. Maybe it's the cold, or the extra time the dish spends soaking in the seasonings. Maybe some of the simple sugars have started to break down. Maybe it's as simple as yesterday was a bad day for ground cow mixed with tomatoes or that today no one says I "have" to eat it. Something happens between the time food is served and the next morning that makes it infinitely more appealing.
Guess what? Writing works the same way.
Hate your MC? Think that you've just burned four hours cranking out a few thousand words of drivel? Forgot what momentary mind lapse made you think this was a good idea? Wondering if McDonald's is hiring because the paper hat would bring in more than you've earned writing so far?
Let it set and walk away.
Take your MS, put in that Ziploc baggie called a file folder and store it in that big and not so very cold fridge you call a desk. (It's that big lump of wood your computer sits on. The one that means you can call your corner of the kitchen a "home office".)
Go do something else. Take a walk, outline a new novel, or learn Portuguese, it doesn't really matter so long as what you're doing doesn't involve looking at that stack of papers in your drawer. Don't touch them for at least 48 hours. They're marinating. (And if you want to know what happens if you disturb the marinating, just picture a really angry Martha Stewart facing off with a really angry Gordon Ramsey... *terrifying*)
Once the time's up, take out the pages and read it again (this is the "sniffing" part where you open that corner of the little plastic box to make sure what's inside doesn't have fur). Most times, you'll find yourself shocked at how likable the MC is. That drivel may still not be so great, but it's no longer cause to toss the MS (and the computer that spawned it) through the nearest shredder. (Shredding a computer is never a good idea, btw, it's very difficult to get the speakers through that tiny little slot.) Your idea is still viable.
Now put down that cold chicken leg and get writing!
Leftovers are just yummy.
(Unless it's Mac & Cheese. No amount of cold congealing or setting in the fridge can make something that looks like slime covered maggots palatable... and for that I blame watching The Lost Boys when I was a kid and seeing the noodles turn to worms. TMI? Probably.)