Confidence in Workouts

During this past training cycle I've noticed that my workouts are going particularly well. When I do a workout at a really good pace it generally gives me pretty good confidence about my racing readiness, but doesn't get me too excited. 

My last training cycle I went through a lot more highs and lows of workouts than my current cycle. I'd do awful at one workout and my confidence would be shot. Then, I destroy another workout and I'd feel a little better. I remember doing a long run where I was supposed to finish the last 10 miles at MP. I ran the first couple about 15 seconds faster than MP and dragged in the last couple over 30 sec slower than marathon pace. It was a pretty hot morning (for Minnesota) and I ran out of water with 6 miles to go. Still, that run definitely took a lot of confidence out of me.

Then, I did the famous (or infamous) Yasso 800s the next week. I hit 10 at an average of 2:57. The goal was for 3:05-3:10 so I was feeling pretty great and a little more confident about being able to run my goal for the marathon. I wasn't, however, so confident that the poor long run didn't continue to bother me.

In general a poor workout drains the confidence out of me much more than a good workout improves it. Today I'm running 4 X 1 mile @ 10k pace, which is about 6:30 / mile. If I blast those miles out at 6:15, I'll feel great but I won't start planning to knock 5 minutes off my goal marathon time. On the other hand, if I run the last 2 at 6:45 and 7:00 I'll definitely start to question myself, although at least I'll be able to tell myself I have 10 weeks to improve.

Does this mean I'm pessimistic or realistic? I don't talk to enough other runners anymore to know if it's normal to let a bad workout affect me more than a good one, but I have a feeling it's not unusual.