Perhaps a lot of it is psychological. But a lot of products like jacked have stimulants in them that are more than just beta alanine or arganine. Its these other stimulants that I imagine I build the tolerance for if I take it for too long of a period. I find with most pre-workouts I have to up the dosage to feel the same intensity.
On a side note, I am wondering, I thought you did build a tolerance (or diminishing returns) from aminos (e.g. creatine) and that was the purpose for cycling.
I know you will laugh but I heard a guy in the gym go so far as to say he feels the effect of taking protein powder is diminishing - so he cycles it. (the dude is a giant)