This is an interesting article i found on PsyBlog

Talking to strangers is more fun than we predict because showing off makes us feel good.Here's an easy choice: would you rather spend 4 minutes chatting to a good friend or to a complete stranger?

It's safe to say most of us would choose our friend. When you chat to someone you know well it's comfortable, relaxed and familiar—with a friend we know what we're getting. With a stranger, though, anything could happen.

In their research Dunn et al. (2007) had participants in long-term relationships predict how pleasurable it would be to interact with:

What the researchers found was that it comes down to whether or not you're making an effort. Sometimes when we talk to our friends and partners we don't make much of an effort to entertain them, show off or to present ourselves in the best light. But we do tend to make more of an effort with strangers.

There's a fascinating point that comes out of this research. When we predict how fun talking to a stranger will be, we fail to factor in the extra effort we make. But when we think about our partners we fail to factor in how lazy we tend to be.

There are two morals to this story: the sad but unsurprising fact that we take our partners and friends for granted and the less intuitive idea that strangers are more fun than we imagine because showing off makes us feel good.

Read the full article (yes this is just a summary) here: Stop Being Socially Lazy and Start Enjoying Yourself