Well. Optimism is key here. You know the saying "Every cloud has a silver lining." Well that basically means, anything shitty always has something good about it. Now, you gotta find that silver lining and focus on it rather then the cloud.
Say you're having a shitty day at work, customers are being bitchy, and you're tired. Now you could call the money you earned a silver lining but that gets old. If you look deeper, you can see what you get to do after work. I work at a gas station, outside. Right now, its averaging -25 degrees celcius and this part of Canada I live in is windy. A couple days ago, I had to work 2:30pm - 10:30pm. It was -27 with a windchill of -38. There were non-stop customers from 3pm till 8pm. I had begun developing a cold in the morning and was already tired from studying the night before. At the start of the shift, I was in a poor mood, felt bad, and hated every customer that rolled up. But I found some optimism in the situation. At 8:30, I get to go inside where its worm and work independently, cleaning up the store. At 10:30, I get to go home and I don't have to go to school the next day. The rest of the night went by better with me knowing that in only a few more hours, I could rest in my nice, warm, comfortable bed.
TL;DR, be optimistic and you'll find life a whole lot better.