[fredwu]

Are these even gotchas if they are all very well documented in the official documentation already? I was expecting to see some unusual or undocumented behaviours...

[lawn]

They are gotchas because they're unusual and people unfamiliar with the language will get confused by them.

I'm sure everyone who has used Elixir has been bitten by the list of numbers to string conversion.

[vendiddy]

They are I've been asked about several of them from beginners.