This is false. They are not allowed to do whatever makes them happy and the example can be that if someone is happy when they commit bad deeds like theft or murder, they are forbidden from doing that. The concept of being free to pursue happiness works when your personal happiness doesn't infringe upon other people's personal happiness. That means that if you like becoming a business man you can be so and if you want to buy a house you can do that, but if stealing or killing makes you happy, you would prevent others from their right to life or the right to pursue happiness so that would be forbidden.
