Being assertive enough to avoid being coerced into sex sounds like a good skill to learn. But you have to wonder what the corresponding page on Challenges said: Try not to rape your girlfriend?

This approach seems self-defeating when you consider that the goal is love - opening and merging your one life with the lives of others. Love requires openness. The point is to be changed by, and to witness change in, one another. Slowly, this back-and-forth transforms the shared reality we call the world. Love is less noun than verb: not a thing to get, but a process to set in motion.

While it might have surprised onlookers, undergraduates in the 2000s were in fact having less sex than their predecessors in the 1980s and '90s - if you accepted their definition of sex as vaginal intercourse. (Those of us who grew up during the Clinton years learned from our president that activities other than intercourse do not constitute "sexual relations," however intimate they may be.)