Very specific examples I have personally witnessed would include:

• People getting angry/irritated when they see young people exiting a car parked on a disabled spot without any obvious impairment or disability.
• People in public spaces (museums, tourist spots, etc.) taking it for granted that if they just saw you climb a few steps, that means you are necessarily able to climb 50 steps without any issues.
• When someone asks if there is a place to sit in a public building/area, staff/officials will often just answer “no, sorry” without considering that the person may actually really need to sit, even if they don’t have a cane or something similar (in which case, they are often much more accommodating)

These are anecdotal, and specific to people I know and their disabilities, but I feel they illustrate how it’s always good to just take a second to think about this sort of thing. It’s also usually a good idea to just ask, instead of assuming.

It’s estimated that around 80% of disabilities are invisible. Also, many disabilities are intermittent or contextual.

It’s always good to keep this in mind when you interact with people you don’t know, regardless of what they seem to be able or unable to do.