Why did my tire fail? Just got back from a ride. On my way back, my rear tire suffered from a side wall blow out. The area that went looks like it has been completely shredded. 

The area feels like it's been melted, with sticky melty rubber covering it.

The tire itself hasn't done 500km, I got it last summer, but haven't been able to ride much. There really shouldn't be any reason I know that the tire failed.

The tires are Michelin Pro4.



Just so you know, each of those fibers had come apart completely.
Two common possibilities:


Your brake pad is contacting the sidewall of the tire. Classic cause for a blowout.
You've used something like heavy-duty engine degreaser to clean your drive train. This will chemically change the rubber and it will remain "tacky" forever. The best degreaser, that won't damage rubber is kerosene+lemon juice (or if you want to spend money, prepackaged citrus degreaser).