All happiness is temporary because it's a feeling you get when certain chemicals are released in your brain. The only way to feel that constantly would be if your brain were damaged in such a way as to constantly produce these chemicals, but even then you would grow a tolerance to them or the feeling they produce and thus would end up not being happy anyway. Thus all happiness is temporary.
There are differing levels of happiness, but they're all still happiness. The feeling derived from completing a small task at work and the feeling derived from getting a promotion and a big end of the year bonus at work are the same feelings, just differing magnitudes. Same goes for feelings of happiness caused from two completely different kinds of events. There is no cause for happiness that is real while others are fake, happiness is happiness.
It is possible to do things yourself, to get things yourself that make you happy. It is indeed possible to attain happiness. This is a basic fact of physiology: you can do things by yourself that cause those chemicals to be released and give you that feeling of happiness.
So, what I'm getting at here is that as usual you're wrong with your banal platitude. You would have a better chance of arguing this if you used another term that meant something along the lines of feeling fulfilled and content with your life. Happiness is a fleeting thing, not a permanent state of feeling good about life as you seem to be positing in the thread. Even if it were you'd still be wrong because it is indeed possible to work toward fulfillment rather than simply accepting that you're fine as is.