He may be very uncomfortable with something that may feel moderately soft to you or he may be waiting for the very stiff brush that he thinks is coming. Put yourself in your horse's place, exactly and moment by moment. Imagine that you are the one being tied, brushed, washed, pushed or pulled. Try to not be judgmental, just try to see what's really going on. After you put your horse away for the day, write down your observations .
Journals can be very helpful in the learning process.
They can be invaluable for looking back and charting changes and progress. They can also remind you of what works and what doesn't. After you write down you observations from the day, consider what you saw. Improving grooming is an important first step in the partnership process. Think about what you can change in your grooming routine that can improve one of the behaviors you saw today and would like to change.