Do you think pessimism is bad? I don’t think so. I have found in many situations that being pessimistic helps out. I am a programmer, and a pessimistic one at most times. In many programming situations, I tend to be pessimistic which helps to figure out loopholes.
The problem with pessimistic attitude is, when one allows it to overwhelm one’s mind to such an extent that it prevents one from taking an action due to fear of negative result.