Here’s something that puts a wrench in your idea: disabled people exist and are often denied immigration explicitly because of their disabled status. Statistically everyone is simply not yet disabled. Some people are just disabled earlier in life than others, permanently affecting their capacity for work, immigration, or other self improvement without external assistance (such as medical intervention, without which they would die). In the disability community there’s a lot of just plain luck: how severe is your condition? How much support can your family supply? Are you in a country with a robust healthcare system? Are you able to afford medication, or are you able to dedicate the time to fight for medication, medical equipment, etc? Does your country have accessibility laws?
And before you call this defeatism: actually pushing harder than is realistic usually makes disability much worse! It’s instead important to realistically understand what’s available to you and frankly speak upon factors beyond your control. Otherwise people end up despairing and killings themselves way more, because they keep setting up expectations and blaming themselves when their circumstances prevent them from doing things they used to do before their disability.
Isn't this kind of a motte and Bailey fallacy, though? You mention disabled people (a population of millions in the world) as your example of luck, but use it to justify the idea that you have to be born in a stable country with resources (arguably disadvantaging almost all of the world's population except for a billion or so).
Those are not even remotely comparable conditions.
And before you call this defeatism: actually pushing harder than is realistic usually makes disability much worse! It’s instead important to realistically understand what’s available to you and frankly speak upon factors beyond your control. Otherwise people end up despairing and killings themselves way more, because they keep setting up expectations and blaming themselves when their circumstances prevent them from doing things they used to do before their disability.