Organizing without first capturing & clarifying what needs organizing is simply rearranging your angst. - David Allen

"Organization" for most people is simply an incomplete list, or amorphous piles, of still-unclear commitments.

Simple, clear purpose and principles give rise to complex and intelligent behavior. Complex rules and regulations give rise to simple and stupid behavior. — Dee Hock

Most often, the reason something is "on your mind" is that you want it to be different than it currently is, and yet:
• you haven't clarified exactly what the intended outcomes is;
• you haven't decided what the very next physical action step is;
• and/or you haven't put reminders of the outcome and the action required in a system you trust.
That's why it's on your mind.