When you carry gear and Stress that exceeds 12 Weight, you become encumbered. While encumbered, you receive a -1 dice penalty to all rolls and cannot push yourself, assist others, or use any move that could make you gain Stress.

An item is 1 Weight if you can hold it with one hand. If it requires a full arm to carry, it’s 2 Weight (and if it requires both full arms, it’s 4 Weight). If it can be held inside a closed fist, then it's 0 Weight.

Stress is an abstract measure of your physical and mental exhaustion. It is something you carry, with a weight all of its own. Each Stress is 1 Weight.