As any seasoned long distance runner would tell you, throughout a training cycle, you must step back occasionally. It is a natural scheduling tool to build your long run up over progressive weeks and to step down every 4-5 weeks. This is done to allow the body to adjust and to recover while still benefitting from distance. I ran 10 miles two weeks ago, 13 miles last weeks, and today, I stepped down to 9 miles. Looking ahead, I have two long runs left before my taper and I will ramp back up to 15 miles next week and finish my long runs with 18-20 miles in two weeks.
I had planned on doing 15 today, but some scheduling issues arose. Consequently, I simply switched today and next week. I was going to pull it back next week, but this will work out just the same. The key remains building miles, avoiding injuries, and increasing the time on my feet. All three of those are currently going well.