A little bit is okay. I forget this. I set a 5 mile PR in February that projects out to better than my marathon goal time. Then, excited by that success, I pushed hard in my next sprint workout. Then I ran marathon-pace miles in my long run. Then I pushed hard in my next tempo workout. Then I had a week of cutting down to half my miles followed by two weeks of absolutely nothing faster than 1+ minute off goal marathon pace as I recovered from the beginnings of a hamstring injury.
I feel fabulous now and training is going according to plan. But it was a good reminder to chill. Giving 100% effort all of the time is a great way to burn out, mentally or physically or both. There is a time and a place for maximum effort, and that should be the only time when I am willing to sacrifice important things for results. Races are followed by recuperation, not more forced effort.
This applies to life as well. This is another step in my endless quest to develop patience and practice strategic action instead of immediate maelstroms. I feel like I'm going to be a really functional person when I'm 60.