Many disabled people have never met someone with the same disability. This is particularly the case, if the disability they have is quite uncommon or there just aren’t any other people that live locally with the same disability.
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I feel this is actually more common than not, many people do not take the time to understand disabilities. However, I really want to work with children with disabilities so I try to take the time to truly understand someone's disability in order to be respectful, but also understand them to some capacity.