Two friends wanted to increase their exercise effort.
One decided to commit to 20 minutes each day (be it walking, jogging, swimming etc).
The other wanted to do this as well. Now knowing these ladies like I do, I figured this was going to be a doomed effort.
SO, I suggested that for each day they did not do their 20mins, they had to put $2 in a jar (small price to pay one would think).