There's an old saying that some days you eat the bear, and then some days the bear eats you. I used to think it was a stupid saying when I was younger, but the longer I'm around, the more I can see the wisdom in it.
Throughout my writing career I've had times when I feel like I'm on top of the world, and other times when I feel like the world's on top of me. I used to sit around and worry when it was the latter of the two feelings, because I thought I was doing something wrong. Experience has taught me that worrying is the worst thing you can do.
Now, when I feel like things are stacked against me, I focus on the good things that I've experienced in the recent past. I then use those items to inspire me to push forward. After experimenting with the ups and downs of my work, I've concluded that if I push just as hard when things aren't going my way as when I can't seem to do anything wrong, I actually gain quite a bit of forward momentum. That probably doesn't sound profound at all, but I was like most people not that long ago: when things got tough, I got down on myself and stopped pushing as hard.
With this new attitude, I've seen a level of success that I used to only dream about. I'm convinced that this is one of the things that separates those who are truly successful from those who aren't. You can define success in a number of ways, so take that for what you want it to mean.
The real test is not agreeing with what I'm saying when you feel all fired up and ready to take on the world, but rather putting it to the test when it seems that even the birds won't sing for you. It's not as easy as it sounds, but with practice and persistance, it can be done. It took me a while to get going, and I'll fully admit that I'm still not perfect at it, but I've become far better at maintaining my forward momentum.