While some have deviated from your original options I will do the same. You originally stated, "assuming your aim is correct and your stroke is straight", I will add an option that causes most missed shots.For a relatively experienced player, assuming your aim is correct and your stroke is straight, in your opinion, which of the 3 variable miscalculations causes the most missed shots when applying spin to the Cue Ball?
Refering to Zerksies post 103...I think most shots are missed by folks taking their 'eyes off of the spot on the object ball' during the last split second before the cue strikes the cue ball.