I dont worry much about bad workouts - they typically tell you that you need rest. It's not as though fitness just disappears, although it might get clouded in fatigue or other life stresses. I believe this to be a downside to the powermeter training, we get too #s oriented and when things are going up, we get too optimistic, when they go down or stagnate, we panic and get too pessimistic. When really, they're just #s and will vary from day to day just like the S&P500.
I do get annoyed at myself when I screw up in preparation for races, mentally, or strategically. As has been the case a couple of times this year, but if I dont have the legs, well, I just dont have the legs - on race day, there's not much you can do about that.
This is supposed to be fun folks, #s, results, upgrades, dont really matter that much, and although emotionally it's natural to get overly involved with results from efforts you pour yourself into, it helps to take a step back for a reality check from time to time.