How do I know if I have a good model?

I built quite a complex model and spent some time testing it and tinkering with it. The results are stable and there are no anomalies. However, I feel like it's too simple, even though it definitely isn't, because I feel like the big guns have infinitely more complicated models. Moreover, I don't know how much profit a good model should simulate. It doesn't make any profit in the same day, but the profit percentage increases linearly with the number of days it's simulated on.

I've worked quite hard on developing it, but end up simulating like 10% profit over a 14-day period. I have no idea if this is good or bad. I also don't know what a good model should generate, what a great model should generate, what other metrics I should look out for, and what features and analyses I should have in place. Any help appreciated!