My cheap pork shoulder turned into a dry brick yesterday

I was so pumped because that big hunk of meat was on a crazy sale, you know? Tried to slow cook it all day to make it tender. Forgot to put the lid on right for like an hour, I think. That was all it took. Ended up with this tough, stringy thing I could barely pull apart. Had to drown it in a vinegar sauce just to get it down. Feels bad wasting a good deal because of one dumb mistake.