If you have a desperate need to know why, then this book has a lot of science, which always helps you to understand what's happening, so long as you have a science degree (luckily I have, but that's beside the point). At the beginning there is a list of 28 figures, the most esoteric of which must be: 10, The formulae for progesterone, norethisterone, and testosterone. Despite being a molecular biologist, knowing the molecular formulae for the hormones involved does not stop you crying because you're lonely, bored and hate your life. I think it might be useful for the professionals to read, but don't expect any hands-on real help.