Indeed. You frequently hear "Everyone is different", "Symptoms can vary" and "Everyone acts differently to XYZ treatment".

But perhaps these are all symptoms of diseases and combinations of diseases varying, rather than the people?

“ Although rare diseases may be individually rare, they are collectively common, with 1 in 17 people being affected by a rare disease at some point in their lives. ”

https://www.gov.uk/government/publications/uk-rare-diseases-...