Answer:
Bad posture, Depth perseption faults, and... uhm, tripping? I don't know a third one, sorry
Step-by-step explanation:
Bad posture could make it go to the left or right and it'd have a chance you would give it less momentum. Depth perseption faults could make you think you're throwing it far but it's a short throw or you could overthrow it, essentially missing the target entirely. And the explanation of why i chose: I don't know a third one, sorry, is because I'm tired. Hope this helps :)