Some situations can give you disadvantage on checks, for example, if you want to pick a lock in a rush or if you want to make a handstand while on a rocking carriage.

If you have disadvantage, roll twice and take the lower result. The higher one is discarded.

Example: To jump over a chasm, you need to pass a Body STR - check of 14+. Between you and the other side is a waterfall that you have to pass through. The GM decides that you have disadvantage as a result. You now roll 2d20 = A 6 and a 15. Since 6 is the lower number, you have to take it and add your Body STR, which is 2. Your final result is 6 + 2 = 8. You fail the check and get thrown into the depths of the chasm by the force of the water.