Though sex typically only takes place between you and your partner, in a psychological sense, your bed is positively crowded with other people in your life who influence what you say, what you do and what you like.

Next time you have an amazing - or rotten! - time in the sack, think of who else you have to thank...or blame.

Surprising Sex Life Shaper #1: Your Ex

We're shaped by our past experiences, especially in the bedroom. The relationship may end, but the feelings it created about our bodies and about sex stay with us. Good and bad relationships can haunt us. Critical lovers may set us up for a future of feeling sexually insecure. Or we idealize the amazing sexual chemistry we had with one ex, setting the bar out of reach for new partners.

Surprising Sex Life Shaper #2: Friends

In our youth, it was our friends who gave us the real lessons in sex education. We learned how to kiss (and more) by sharing knowledge in abandoned playgrounds. Your grown-up sexual self owes them a lot. Just don't let your friends interfere now that you're all grown up. Hear your best friend recount the details of a new sexual conquest, that kinky thing they did and just how wonderful it was to do it, and it's hard not to suddenly notice what your relationship lacks. We know it shouldn't matter...but it does.

Surprising Sex Life Shaper #3: Celebrities

From the silver screen to the small screen, we see them: perfect bodies and flawless faces, reaching mind-blowing simultaneous climax, under soft lighting and in flattering poses. Is it any wonder we don't think we measure up? We know real sex is nothing like the fantasy version we see on film. But because we never (or rarely) see real sex - the kind with cellulite, fluorescent lighting and bed head - we're left feeling vaguely flawed and dissatisfied.

Surprising Sex Life Shaper #4: Mom & Dad

Gross, we know. But just like inheriting Mom's green eyes or Dad's gap-toothed grin, you also get sexual traits as genetic legacies. Your DNA influences your personality, your relationships and your sex drive. Of course, it doesn't end there. How you were brought up - whether your folks enforced a no-dating rule or handed out condoms to you like candy - and how your parents treated each other all factor into how you behave in your relationships today.