So if multitasking leads to a weak frontal lobe, does it promote blanking out too?

If you've ever forgotten what you are reading in a chemistry book, or lost your chain of thought mid-sentance writing a paper, you know what I mean. Why do other parts of the brain hijack the frontal lobe so easily at some activities but not others? Thats literally what it feels like to me.

I can pinpoint exactly when I'm about to procrastinate to a moment when i forget what im writing. Its when my brain wants to look for something else to do, to think about, but i don't let it. i wont let it go there, so it hovers in limbo for a second. It really tries to reject my current activity.

However I was kind of undisciplined as a kid.

I wouldn't say I'm ADD because i can concentrate on certain things for hours. When it comes to certain jobs however, it depends on the day.

If the brain is programmed to disengage when its bored, because it finds boring material irrelevant for survival how do you bridge that gap ?

I can care about activity B a lot if its relevant to a job. But thats not always enough to be completely submerged. Yes i can recover from getting side-tracked sometimes but why get side-tracked at all? So can anyone studying the brain lemme know?