It doesn't. It only depends on subjective uncertainty (limits on predictive accuracy in some context), which looks similar to "randomness" but is not.
First, think of a random number from 1 to 10 and remember it. If random forces don't exist then all energy in the universe has one preordained future. In theory this could be calculated ahead of time. Since we are made of this energy, we also have one preordained future that cannot be changed. Knowing this we could change a decision, though this modification was preordained. So our sense of free will is just our imagination. Is the number you picked three? We are not so random after all.