The more you overcommit, the more that procrastination becomes intolerably expensive to engage ... yet it is when procrastination becomes exceedingly costly to do, it is then that extreme creativity emerges. In the impossible moment, miracles tend to happen. "Necessary procrastination" is a prime factor in the creative process. When the cost of procrastination increases, the probability for radical new thoughts to emerge increases as well.
If you want something particular done, asking the busiest person you know is no guarantee. But if you want something done, ask the busiest person you know. Something will happen - perhaps not what you originally intended, but something.
This may be the source behind my drive to overcommit, which I know is shared by plenty of other Oliners and IMSAns. Squeezing in heartfelt late night conversations between overdue problem sets makes them that much more costly, and therefore much more meaningful. Side projects smuggled in the back of lectures mean they've got to be worth your time enough to pursue despite the cost of missing information. It's a natural pressure cooker to inspire and winnow out the extraordinary.