True happiness doesn't need any validation from external people or achievements
Just because achieving your goals won't bring you happiness doesn't mean that a total detachment from the world is a sign of true contentedness. Humans need connection, and it's not a sign of unhappiness if you happen to want a family or really take pleasure in getting a promotion at work. Don't confuse this with a romantic connection, though -- the essential thing here is that connection makes you more human, whether that's through platonic friendships, volunteering, stamp collector swap meets, a backgammon club, or whatever you enjoy.
Happiness is merely a state of mind
There are few things that get me more riled up than "inspirational" quotes like "Choose happiness" or "It’s all in your head." You know how that makes a person with depression or anxiety feel? REALLY FUCKING SHITTY.
Of course your outlook has a significant impact on mood, but so do hormones, neurotransmitters, sleep, exercise, diet, drugs, breakups, death, stress, transition, that John Cusack movie you can't stop talking about -- you get the idea.