While I was preparing this post, I found that people are getting tired of this phrase. But that's because they hear it so often, so it's certainly an idiom that you want in your repertoire. (The next most confusing thing about English besides the idioms is how much French there is in it. lol)
Person 1: No matter how hard I try, I can never seem to make breakfast in the morning.
Person 2: If you would just get up 15 minutes earlier, you could do it. It's not rocket science!
A related idiom is It's Not Brain Surgery.
(Just for the record: If anything ever involves getting up 15 minutes early, it might as well be rocket science for me. lol)
Tune in tomorrow when I will explain the idiom, Just for the Record.