I saw this sentence in an episode of Attack on Titan
A character that is believed to be selfish does something perceived to be selfless by the the speaker, and the speaker says
自分のことしか考えてない男のはずだ
which was translated in the subs to mean
The Jean I know is someone who only thinks about himself.
Why use the negative 考えてない in this case? Wouldn't that mean he doesn't only think of himself? How is it different from using 考えてる or 考える?
