For most people in most situations, I believe the optimism exercise is a good thing.
For me, it has become a source of stress and anxiety. According to the description, the exercise should be take two minutes each day. For me, it has required multiple hours each day because I must deal with anxiety. If those were the only issues, I would continue with the exercise.
In about one week (or less), however, I will be at another major crisis point. I must use my limited strength to deal with multiple, pressing issues.