Does this ever happen to you?

You have this trilogy (or pick any number) planned out, and you're writing number 1, which is cool and interesting and stuff (at least you hope it is), but what you ACTUALLY want to be writing is number 3, because that's where things gets really juicy/heat up, and it has all the awesome scenes that were the first ones that popped into your head and gave you this whole idea, but you CAN'T write that now because 1 comes before 3 (yes, it does. I'm a maths teacher, I...