Shocking fact -- Life is only about 900 months.
Draw a 30x30 table on paper. Check one box every month. Thats your whole life.
"900 Months" helps you to remember this fact, and to have a clear view on you lifetime. Every month, review the 900 boxes and count how many boxes are left unchecked. Thus, as Thoreau said, "... and not, when I came to die, discover that I had not lived."
Tips: Touch the boxes, touch the tombstone.