Specifically with the following sentence, which is more suitable/correct?
You don't count on humans to not do things they're used to doing.
You don't count on humans not to do things they're used to doing.
Specifically with the following sentence, which is more suitable/correct?
You don't count on humans to not do things they're used to doing.
You don't count on humans not to do things they're used to doing.
You don't count on humans not to do things they're used to doing.
Either are okay.
One "textbook" (possibly outdated) rule is never to break up an infinitive (or to never break up an infinitive). However, at least in modern American English, this rule is followed or not followed as if there wasn't any such rule at all. In other words, whether to use "not to do" and "to not do" seems to come down to personal preference for many.
Nowadays 'to not do' is acceptable in less formal contexts, but 'not to do' is still the first choice in more formal ones.
Google Ngram Viewer shows that, even now, 'not to do' is hundreds of times more common than 'to not do'. The use of 'to not do' is growing, but the use of 'not to do' is growing even faster.