Sometimes depressed people depress themselves more because they dwell.
I'm not saying accept a bad situation and just hack it.
Happiness comes from inside. Sure there are factors on the outside that can annoy you or irritate or pull you down but to generate that good feeling, it needs to come from inside. I don't think you can rely on outside factors alone. A new job, gf, victory... all may help but I think happiness will always be a state of mind we need to work on to achieve.
Sometimes it is easier for others. I think those people know how to look towards positives and opportunities, while the sad ones see the darkness. Perhaps a bad situation masks the sunshine, but hope can light the way.
If you show too much sadness on the outside, or negative energy, other people around you will be brought down too. First you may get sympathy, but if you continue, It becomes unattractive so may worsen your situation.
Whereas if you are cheery / positive, when times are tough, people will admire that. The positive energy will be inspiring and bring people around you up, instead of down.