For me that's the acid test: whatever it says on your passport is your real name. Today I learned that I don't have a real name. More seriously, though, most

For me that's the acid test: whatever it says on your passport is your real name. Today I learned that I don't have a real name. More seriously, though, most people I know IRL insist on not going by the name on their passport. If I had one, my name would be "Christopher", but I insist on "Chris" enough that I will not make my name "Christopher" on Google. For a less silly example, though, most people I know whose names are not derived from their full legal names are some form of non-cisgendered people who simply don't identify with their given names. And, in the US at least, for most purposes it is simply not necessary to go the court-decreed route (we don't have a strict equivalence of a deed poll form for name changes as far as I know) and bringing court and public record into things can be unnecessary trouble until they fall out of those "most purposes". Of course, these are only a couple of reasons why one might wish not to use their passport names online, but the main point is: it's rarely as simple as you think.