The secret to desire in a long-term relationship, a TED Talk given by psychotherapist and relationship expert Esther Perel explores the question, “how do love and desire relate?"

Perel explains that love is to have, but desire is to want. And if you want to have a vibrant, long-lasting love relationship, you've got to watch it.

We want our spouse to be everything to us, Perel explains— to love us unconditionally, to be faithful, to care for and comfort us, share responsibilities with us, to give us equality, to help form our identity.

But we also want, and expect, this person to surprise us, keep us on our toes, provide mystery and edge.

Perel explains that we have two fundamental—but competing—needs, our need for “security, predictability, safety, dependability" and our need for “adventure, novelty, risk, for danger, for the unknown, for the unexpected."

This intriguing talk explores the question, “how do we combine our need for security with the need for adventure into one passionate marriage?"

Here are the bedroom secrets of happy couples. . .

1. They have a lot of sexual privacy:

They understand that there is an erotic space that belongs to each of them.

2. They understand that foreplay is not something you do five minutes before the real thing:

Foreplay pretty much starts at the end of the previous orgasm.

3. They understand that an erotic space is the place where you stop being a good citizen who is taking care of things and being responsible:

Responsibility and desire butt heads, they don't do well together.

4. They also understand that passion waxes and wanes:

It's pretty much like the moon, it has intermittent eclipses. But what erotic couples know is how to resurrect it.