I don't know if you were old enough around year 2000 to witness this whole Florida recount debacle, "pregnant chads" and all that, but this was a good illustration why counting paper ballot is always imprecise, to some small degree. You can alter design of the ballot to minimize factor of randomness, and enforce some strict standards on canvassers, but it will never be zero.

The only ultimate solution here is electronic voting, where voter's intent can't be misinterpreted; however, in practice, people will never trust machines (even with paper trail), because "everything can be hacked". So we are stuck with paper ballots.