Any fool can win a poker hand with a royal flush; good poker players know how to win with lousy hands. This is true of pitchers, too. If you've been pitching for a while, you'll know that some days you feel great. Your fastballs are rockets, your curveballs break just where you want them, you can pick your spots at the corners of the strike zone at will. Some days, you can tell something's off. You throw lots of wild pitches, your fastball feels weak, you're unconfident that you can even find the strike zone. Some pitchers refer to these kinds of pitching days as "good stuff" and "bad stuff."
As a young pitcher, you're probably going to have more bad stuff than good. That's not the end of the world, it's just part of your development as a pitcher. Even pros have bad stuff. They don't flee the mound, they fight through it. You've got to do the same.
If you're having an off day on the mound, that's when it's really time to focus. It's the perfect time to use the other strategies in this article, because you're not going to beat the batters with raw skill. Forget about bad pitches you threw in the early innings. Focus on one batter at a time – set him up, use your defense when you can, then move on to the next batter. Focus on each individual pitch, and don't worry about throwing a perfect pitch. Pros don't throw perfect pitches. Shoot for good pitches.
One thing you can do when your fastball isn't so fast is to adjust and throw a bit lower. Most batters love a high pitch over the plate, but if you keep them low, batters will tend to hit more infield ground balls that your defense can turn into outs.