Happiness is often about having an impressive life, when we feel joy we see that our life is seamlessly part of everything else. When it comes to worldly happiness, there's always someone with a fancier title or a nicer house. Joy is personal and can't be compared to anyone else's. Being in nature is full of joy. There's no good or bad way to look at a beautiful landscape. No one will outcompete your appreciation of natural beauty. Conventional happiness is too much like doing accounting on your life and hoping that you come up with a positive number. Joy is forgetting that and appreciating what's right in front of you. The experience of seeing a beautiful wildflower in early spring is only enhanced by knowing that it will soon fade.
Something that I've been learning to appreciate is that this practice is more than just words. The idea that you should have a loose handle on conventional happiness/success has real practical implications in Soto Zen. Beginners and experts alike all engage in "just-sitting" meditation no matter how long they've been practicing. We don't talk about whether we are good or bad at sitting, we just sit with whatever is coming up for us at the time.
So maybe, at least once in a while, stop trying to measure your life and just appreciate it for what it is. You might find your daily experience is suffused with joy without you even looking for it.