The Physical Laws of Backpacking:

1. The integral of the gravitational potential taken around any closed loop trail you choose to hike always comes out positive.*
2. A stone in your boot always migrates against the pressure gradient to exactly the point of most pressure.
3. The weight of your pack increases in direct proportion to the amount of food you consume from it. If you run out of food, the pack weight goes on increasing anyway.
4. The number of stones in your boot is directly proportional to the number of hours you have been on the trail.
5. The difficulty of finding any given trail marker is directly proportional to the importance of the consequences of failing to find it.
6. The size of each of the stones in your boot is directly proportional to the number of hours you have been on the trail.
7. The remaining distance to your chosen campsite remains constant as twilight approaches.
8. The net weight of your boots is directly proportional to the cube of the number of hours you have been on the trail.
9. When you arrive at your chosen campsite, it is full.
10. If you take your boots off, you will never get them back on again.
11. As you settle down for the evening, the local density of mosquitos will be inversely proportional to the amount of your remaining repellent.
12. The probability that a bear will get your pack during the night starts at .5 and rises asymptotically towards 1.0 as the number of hours you put into bear-proofing the pack increases.

Footnote: I wrote the first 10 of these laws sometime in the 70's, during a particularly arduous trek in the Sierra's, and then I posted them on a bulletin board at Control Data. Some years later I discovered them, properly credited to me, published in a very funny book by Paul Dickson entitled "The Official Rules" (Addison-Wesley). I have no idea how they found their way to the book.

*Translation for those who don't speak physics: The "gravitational potential" is a measure of the energy due to gravity. It is a law of nature that the integral of the gravitational potential taken around any closed loop is zero, i.e. there is as much downhill as uphill in any loop. Law #1 is a fancy way of saying that any loop trail you choose to hike will have more uphill than downhill (no matter which way you choose to hike around the loop).