I don't think there are any negative affects of a true positive thinking. What happens though is some people believe that positive thinking is denial and that's the important distinction to make. If you are in denial about something, let's say you have some kind of addiction whether it's smoking, drinking, drugs or gambling and if you stay in denial about that and think everything is okay and you don't have a problem, that's not positive thinking. Positive thinking would be acknowledging that there is a problem and there is a way to deal with it; thinking "I can deal with this and I will find the right kind of help to help me overcome this."
