Burn-out is an occupational hazard for flight instructors. I vividly remember when I had accumulated my first 1000 hours of "dual given" and thought it was impossible to teach even one more hour. Every time I flew another pattern lesson I felt a creeping rage growing and knew I was "hitting the wall" of what was humanly possible. Now I have over 9,000 hours of dual given. (The lobotomy sure helped!) But seriously, the solution is a cognitive re-framing of the instructional session. We all easily fall into the error of making VFR lesson #7 the same for everyone. We have skills to teach and know the drill so off we go. Big mistake! Every lesson is unique; that is a different person you are flying with possessing unique background, needs and abilities! If you focus (correctly) on this unique student, you quickly realize that you never gave this lesson before and this is all new...to both of you. How can I impart this set of skills, knowledge and judgment to this unique individual given this set of circumstances? Now we are on to something important. We were sliding into dangerous complacency and stereotyping the whole experience into a bad soap opera. When this happens, motivation slides right out the window and you feel entirely useless. Safety is also compromised because we are not going flying with the level of awareness and alertness required to even be safe.
Another method of staying motivated is to actively pursue new learning on your own; "sharpen the saw" as Stephen Covey says. Not only does this expand your "toolbox of skills," it revitalizes you. I recommend trying gliders or seaplanes or some other new flight experience. This not only expands your aviation horizons, it helps you commiserate with your students and realize that initial lack of proficiency is normal and expected. This recharges your batteries and helps you examine the teacher/student role from their angle. I recently took some helicopter dual and in addition to being a (happy) klutz at the controls, I developed great admiration for the CFI who patiently guided me through hovering again. I felt a kinship with my students who tried hard but did not initially succeed.