There are people who are legitimately disabled. They can be denied benefits on the first application. Usually Social Security will send applicants to a doctor at their expense to determine whether a disability classification should be granted.
You have be incapable of doing any kind of normal gainful work to qualify. And obviously, this is where it can get subjective.
We all know here there are legitimately disabled people on it so it’s just a distraction really in discussing fraud. No one is talking about you or your relative, whatever.
The overarching point is there has been a steady increase in SSDI over the years, especially under Obama, and it is NOT due to legitimate disability.