Life's not all about things, however, we as humans have a need for progress. If you are constantly doing the same thing and you aren't challenged, studies have shown that you have a much higher probability of being diagnosed with depression. It's important to consider that we all need progress even if you aren't necessarily after "stuff."
You see fulfillment comes from the inside. When you control your own emotional state, you will find that you can choose to feel any way you want. Now, I'm not gonna say you should be happy all the time, that's a form of psychosis, but what you can do is not beat yourself up when things aren't going your way.