It can, however, usually be found in your experience.
You might not have the same experiences as your protagonists, but it's pretty likely that you do have transferable knowledge. J.K. Rowling had (probably...) never played quidditch--but I bet she knew what it felt like to play on a team, have others relying on her to play hard, to play hard and win, and to play hard and lose. Anyone who's survived P.E. class has that, right? It's just transferring what you already know into understanding what you haven't experiences.
Everyone has unique experiences that lend all kinds of insider's knowledge that can come to play in writing. One of my most common sources of inspiration and intuition is my weird hobby. I do living history events--Revolutionary War reenactment. (Pause for getting over extreme geekiness of previous statement.) Obviously if I wanted to write about the American Revolution or the 18th Century in general it provides tons of great info. But if you dig deeper, it provides a lot more.
So, four ways in which my weird hobby gives me ways to write what I know, even when I don't know much:
|Five mile march...in February. At least it didn't rain too much.|
3) Wearing Weird Clothes. This might seem minor. But every time I read a historical or a fantasy that incorporates corsetry and they get it so, so wrong...I cringe. I know what wearing a corset feels like (it's not bad) and what a few petticoats feel like, too--which makes approaching historicals a little easier. But more than that, I know what wearing different clothes mean--it means moving differently, taking a different approach to getting dressed, and thinking about clothing differently. All this means that no matter what my characters are wearing, whether it's 1800 or some imagined future, I know to think about it, and to think about how it affects them.
4) Something Akin to Combat Situations. It's not the real thing. It's nowhere close to the real thing. I want to be super-clear about that mostly because of the extreme respect I have for anyone who has experienced the real thing. But seeing a facsimile often enough makes you appreciate the realities of the real thing much more. There's the tactile experience--the sounds of orders being shouted and weapons discharging, being uncomfortably hot or cold or tired but having to stand stock still. There's the emotional experience--there are stakes, and you have a job to do. Sure, the stakes are low ones in this situation--but there's still a cranky commander yelling at you if you don't move the cannon fast enough. And then there's the cognitive experience--the way troops move, the balance between order and confusion, seeing tactics in play. You see choices play out and gain such an understanding for how maneuvers actually work and the factors that go into deciding what to do next. Like chess. But with people.
So, one weekend's worth of experience, used four ways. And I might have a somewhat extreme example of a time-engrossing geeky hobby, but I'd wager everyone has something or several somethings like it that they can use to great effect in their writing. What's yours?