In science nothing can be proved. But all it takes.is one data point to disprove something.
I hypothesize that all zebras have black and white stripes. This hypothesis can never be proved no matter how many zebras we observe. But all it takes is the observation of one zebra with purple stripes to disprove the entire statement.
As einstein once said no amount of experimentation can prove him right, but all it takes is one experiment to prove him wrong.
That being said. The hypothesis here is that being smart makes you happy. To disprove this statement all you need is one instance of a person who is smart and not happy. That's it. Keep in mind I never said being smart makes you unhappy.