Emotions is really a big problem with doing trades because it will affect you psychologically and if this will happen to you, you could not able to decide properly and might be derailed on your listed plans or methods that you should do thats why its really hard when you let your emotions overcome you when you are in the middle of a trade.
I've seen problem with people's emotional nature a lot while I traded on my local exchange.
Sometime out of a blue one huge sell order appears, when rest of traders see it some of them lose their composure and panic, setting much cheaper sell orders.
And how chain reaction usually begins - in extreme cases I noticed that BTC price can go down even ~$100 - before someone sane appears an buy BTC from these idiots.