Based on people I have known, either briefly or closely, it seems to be a pretty big roll of the dice, although that is not how it's supposed to be. I have seen people with moderate struggles get disability relatively smoothly and people with severe disability have to fight tooth and nail. And everything in between and vice versa. It seems to be a poorly run system. So if you are struggling and get very judgemental attitudes on your first attempt, don't give up.