Running is frustrating

So I ran the route of my last post again, and began to stretch out my stride and I felt good all the way round. Felt strong, felt like I had good rhythm and fluency. I was hopeful of a good time. 29 min 36 seconds which means yes I was quicker by 6 seconds. 6 SECONDS!!! I mean that's a slow crossing of the road, it's nothing. How does that work? How can I feel so much better about the run and only run 6 SECONDS quicker? Any ideas?