Ruth carelessly parks her car on a steep hill, leaving the car in neutral and failing to engage the parking brake. The car rolls down the hill and knocks down an electric 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?