'Good' emotions (joy, happiness, excitement, etc...) will give a people a false sense of superiority when it comes to their trading and causes people to over trade with the expectation they are going to 'win big' or some other such nonsense.
'Bad' emotions (anger, depression, despair, etc...) will give people a 'fight or flight' kind of response that happens when a trader makes a really bad trade.
This causes people to over trade and make bad trading decisions such as trying to trade themselves out of a bad situation on their account with massive lot/unit sizes and such, which when the trade goes bad, will cause traders panic and blow out their account because are ignoring the basic rules of successful trading.
Emotions should NEVER be allowed to have any impact whatsoever in trading the markets.
If it looks too good to be true, it's probably a scam! Let the buyer beware.