"Your mind is for having ideas, not holding them."
- David Allen

How many times have you had a 'million-dollar idea' and then totally forget it the next day? Or that thing you keep needing to buy at the grocery store, but somehow always miss it while you're there.

Keeping ideas and tasks in our heads is a flawed system. 

Instead of keeping ideas in your memory, you need to find a safe place to keep them—a place where you will look again later and not forget.

Write it down, just in case.