There's a great chart on page 41 that breaks out disabilities into "permanent", "temporary", and "situational". When I saw this, it opened my eyes up to the reality that everyone can and will experience a sub-optimal, disabled experience when trying to use a product. One example from that chart is that you can suffer a permanent sight disability by losing your sight, a temporary one by dealing with a cataract (pre-surgery), and a situational one when you're in an environment with a lot of distractions or poor lighting conditions.
This all underlines the spirit behind "inclusive design": improving a product's accessibility for one person does more than benefit that one person -- it will provide benefits for everyone. In essence, accessible UX is good UX. If anyone's interested in these ideas, I strongly recommend watching Rob Dodson's fantastic presentation on the topic [2]!
[1] https://download.microsoft.com/download/B/0/D/B0D4BF87-09CE-...