Does your horse jump 10 feet every time a stick moves? Does he snort and buck at the feed stack because he thinks its going to bite him?Some horses are naturally timid. Their nature tells them to get away from something they think is dangerous. Also nervousness could be caused by to much energy, bad eyesight, or a nervous rider.
If your horse is very upset and seems genuinely scared, don't lose your temper and smack him, this will just further upset him.
Just talk to him calmly ands slowly let him check out the object. If he doesnt go near it, hop off and lead him over. rustle it with your foot a bit so he doesnt think it is goin to bite him.
Don't forget, even the most level headed horse can get spooked, so always keep a tense grip on your reins and stay alert to things around you.