Ruth carelessly parks her car on a steep hill, leaves the car in neutral, and fails to engage the parking brake. The car rolls down the hill and knocks down a power line.

The sparks from the broken line ignite a grass fire. The fire spreads until it reaches a barn one mile away. The barn houses dynamite, and the burning barn explodes, causing part of the roof to fall on and injure Jim, a passing motorist.  Which element of negligence is of the greatest concern here? What legal doctrine resolves this issue? Will Jim be able to recover damages from  Ruth? Explain fully.