A dude named Mankiw coined 10 economic principles; i've added an 11the because mountain biking is sligthly more complicated than other economies:
1. There will always be a trade-off between different singletracks. To ride some great technical climbies and bridgies at Teak Place, you give up some cool giraffes in Groenkloof.
2. The 'cost' of riding in one place is what you gave up by not riding at another.
3. The benefit of riding always exceeds the benefit of not riding. It's is better to ride just a little bit on a weekend if time won't allow more, than to not ride at all.
4. Mountain Bikers respond to incentives. The better the tracks, company, variety, remoteness, roughness, stories and wildlife, the more riders will want to go there.
5. Trade can make everyone better off. You show me your favourite trails, and I'll show you mine.
6. Mountain bikers attract mountain bikers. The more mountain bikers you know, the bigger the possibility of getting invited to more exciting places to ride.
7. Don't rely on governments and other people to get it right. But sometimes they do (Groenkloof comes to mind)
8. A mountain biking community's standard of living is directly proportional to the variety of single-track close by. Happy mountain bikers are more productive, hence earn more, hence have more time to play.
9. Inflation is when all your buddies ride very expensive bikes, and you have to get a bike with more travel and tyres with more grip, so that you could keep up with them on the downhills. Either change jobs so you can also afford a very abusable High-Tec all-mountain bike and adventures like Freedom Challenge, or change riding buddies.
10. Mountain bikers face a trade-off between riding and working. The ideal is to always be able to ride, but most riders have to work to afford their hobbies.
11. If the spruit is swamped for weeks on end, or if all free time is used up for studies, dabbling into trail running or even just writing about mountain biking provides some relief :)