I'm writing a book. What do you think a spy should know?

Okay, I'm writing a book and would love to hear what y'all think about this. I've read a few teen spy books like the Gallagher Girls series and The Specialists series. Both of these series had a different take on being a spy. What do you think a spy should know? Anything specific like from the Gallagher Girl series or the Specialists series. If you have read any of these books that helps. If your just going to write something like "know different languages, be very fit, intelligent, etc" please don't comment. Please give me your opinion (and please no mean comments) and thank you for your help!!! If you need any info from me just comment your thoughts and I'll add details quickly.