Words can be surprisingly misleading. Are you up for an experiment? Ask three people what they think happiness means. Not what personally makes them happy but just what happiness is according to a dictionary.
For me it was a total eye-opener to discover that lots of people separated meaning and purpose from happiness. That happiness was supposed to mean pleasure and that that comes from meeting basic needs. Now if I tell you that positive psychology is the science of happiness and all you think about is pleasure how could you not think it to be superficial or at best incomplete? If you think something is superficial and incomplete it’s very likely that you will resist learning about it. Which is a shame because meaning and purpose are very much part of happiness, so it’s not superficial and incomplete at all. You will never know that, unless you are open to the idea, that innocent, everyday words can mean something completely different to the person in front of you. Sometimes the sole reason for resistance is differing definitions.