I've had a few dives where we didn't see very much and I had a hard time getting excited. But that's part of the fun of diving, really; it's like slot machines. If they paid off all the time, it wouldn't be as exciting to hit a jackpot.
In our sites, you almost always see SOMETHING. You may have to get excited about why a whole circle of hermit crabs appear to be having a war, or tickling a moon snail to make it show it's shell. Or you can enjoy the profusion of colors and shapes of starfish, or how the little tiny crabs wave their white claws pugnaciously at you, despite the fact that they weigh about half an ounce and would have no chance in a fair fight. You might want to find a specific purpose for a given dive, like mine today, which was to practice with my new camera. Finding dozens of alabaster nudibranchs was a great thing, because they hold still to pose! Or you designate a dive to practice skills, doing them over and over again to try to make them perfect.
Diving the same sites also makes you part of the "community". Today, for example, I knew that at a certain set of pilings, I was likely to see a Red Irish Lord (who wasn't home today) and a scaled crab, who was. We knew if we knocked on a certain door, there would be a Giant Pacific Octopus behind it. You make the "rounds" and say hello to your acquaintances, and get started and delighted by the new guys on the block.
You only get tired of diving if you want to.