Sometimes we have bad days.
For example, I'm not in love with my day job. To put it simply, some days are better than others. Most days the job is 'good enough.' I can work part-time and come home and do what I love: write fiction, blog, etc. But on days when work is particularly bad I have a hard time concentrating on writing. On those days I feel like I'm faced with two options:
1. I can stew over my horrible day, and generally be angry at everything for the rest of the night.
2. I can take some time to be annoyed and then get on with my life. This job was never one I planned on being in forever, so why let it get to me? Why not take this as a sign that it's time to take the next steps forward, and make an effort to improve my situation?
Think about it in terms of getting published: If you get pissed off about every rejection letter, you're not going to get very far in your writing career. On the other hand, if you give yourself an hour or two to be upset and then go back to work, you're going to be a lot more successful that way.
We have to keep moving forward. Even on our bad days. That's the only way we're going to get anywhere.