Wikiphilosophers/Happiness/S. Perquin
I think one can only be truly happy when accepting things as they are. If you accept things as they are and are content with what you have, you don't lack anything. If you feel that nothing is missing in your life, then I think you can experience true happiness. Anything that you have no control over, I think it's best to accept because you can't do anything about it anyway. That doesn't mean you should never be sad or never grieve, but more that you don't deal with it systematically.
Many things not caused by humans are beyond our control, such as the death of someone or the breakdown of a computer. Everything will decay at some point, and we have no control over it. If you are aware of this, you will also stop taking life so seriously. All material things will perish, so why attach so much value to them? If you acknowledge this, I think you will more quickly accept things for what they are.