Good design is mature, it does not allow you to make childish mistakes.
Onur Cobanli explains:
You can take this either literally or not literally; literally, hot minds (brains that think a lot, thus actually getting heated - applies both for computers and people a like) produce cool (great ideas, among of course many others). Then hot minds (smart minds?) can also produce good ideas, perhaps it is both, but I think thinking a lot on the subject is as important as having the capacity to think on the subject.