March 14 PhD comics includes a plot. The x-axis is “time spent staring at your computer” and the y-axis is “probability you’ll come up with a brilliant idea”. The graph is a horizontal line.
This has two possible interpretations:
- the intended one: at least at the time depicted in the comic, no ideas come. this corresponds to interpreting the y-axis as the cumulative probability that an idea will come by time x.
- the hopeful one: let’s say I stare at my computer for 24 hours straight, starting now. The probability that I come up with a brilliant idea between 11:00 AM and 11:01 AM, say, is the same as the probability that I come up with a brilliant idea between 11:00 PM and 11:01 PM. In other words, brilliant-idea-having is a Poisson process. But then if I wait long enough, I should almost certainly come up with a good idea. This corresponds to interpreting the y-axis as the rate of a Poisson process at time x.
The truth is probably somewhere in between: 40 hours a week is as productive as 55. And Cham, we’re meant to understand, is depicting that part after 40 hours in a week where the brain just won’t get more done.
God plays dice 
How about time spent browsing PhD Comics on the x-axis, vs. number of times laughed on the y-axis? Not only is that a horizontal line, it’s one with height zero!