First off, this phrase isn’t what you probably think it is. The version I am talking about is:
On a mission, focused, determined. Popularized by the TV series the A-Team. When Hannibal Smith came up with a plan to defeat the bad guys, they always referred to him as “on the jazz.”
As a big A-Team fan this is a phrase I like using.
It is also a powerful state-of-mind to be in.