When I was growing up I often saw small children running around with shaved heads. The belief was that hair would come back stronger after shaving. I tend to doubt this, since I can't really see how the action of a razor would have much to do with the layer of skin where the roots of the hair follicle are. I suspect that seeing regrowth causes people to think that hair regrows quickly. My wife says that people in the industry (those highly trained hair stylists), will tell you that not even vigourous brushing will help accelerate growth. It's a myth.
The first day, say, it grows 1 mm (far too fast, according to my data so far, but bear with me). The next day, it has grown another mm, to 2 mm. 100 percent growth. The third day, another mm makes 3 mm total length. 50% growth. The fourth day, another mm makes 4 mm total, for 33% growth. etc. etc.
The impression given is that the initial shaving has caused a growth spurt, but in fact we are simply observing a diminishing fraction of total length being contributed by a completely constant growth rate. John Allen Paulos' books Innumeracy and Beyond Numeracy come to mind...
