Let's not forget that optimizing only a few variables in a system as complicated as happiness can easily result in a net loss.

If you optimize a race car's engine for power, the engine will explode and you will lose the race. That's because you optimized for only one variable, and did not consider longevity. With complex systems this is an important concept to remember, as you may not even be aware of some of the variables, and inadvertently sacrifice them!