The missile knows where it is at all times. It knows this because it knows where it isn't. By subtracting where it is from where it isn't, or where it isn't from where it is - whichever is greater - it obtains a- you know what? you already know how the copypasta goes, so I'll explain what the missile actually does.

The Missile™ knows where it is and where it's pointing at, and it knows where you are and where you will be. The funky trees guidance system orients The Missile™ to point at the position where you will be, no matter what. The missile locking system is just simply there to alert you that The Missile™ is now arriving at a position where you will be, and there is not much you can do about it. The only way to deal with this ridiculous weapon is to use even more ridiculous countermeasures. Have fun!

AG-8 to disable Missile Autoaim.

Aircraft used for the thumbnail: https://www.simpleplanes.com/a/dim3H5/Ai-Enemy-Boss-Andrey-Cherlinski