Those of you up on your fairy tales may remember the story of Goldilocks and the Three Bears. As Goldilocks samples the porridge, beds, and chairs of the three bears, she pronounces in each instance that one of the items she has tried is "just right."
The relationship between sexual arousal and anxiety (or risk) is similar. At intense levels, anxiety is the enemy of sexual arousal, disabling the sexual components of the autonomic nervous system and overriding cortical pleasure centers. It's difficult, if not impossible, to be sexually excited and terrified at the same time. At the other extreme, if there is no risk at all, it's often difficult for some people to become sexually aroused or excited. The inverted U curve is an excellent representation of the relationship between anxiety and sexual arousal and suggests that average levels of anxiety or risk create an environment for optimal sexual excitement. Too little risk, no sexual excitement; too much risk, sexual excitement is suppressed.
This risk-arousal relationship explains why some couples who've been married for years suddenly decide to drive out to Lovers' Lane and have sex in the family Buick, like they did when they were teenagers. Others join the Mile High Club and have sex in airplanes, while still others have sex where and when they might be discovered to enhance the risk and thereby increase sexual excitement.
Predictability and sameness in one's sexual scenarios equals boredom and lack of sexual excitement, just as high-risk encounters can suppress sexual expression. Ideally, sexual encounters involve some mystery and something of the unknown (which implies risk), even if the risk is only symbolic in nature.
Stay in the ideal middle of the inverted U curve and experience a more exciting sex life.