I recently posted a casting notice for a new short film project I wrote, and was amazed at the insane number of responses I got. So many, in fact, that it was logistically impossible for me to see even a small fraction of the people who submitted given my schedule. Of those who I did see, all of them were uniquely talented, well-trained, and tenacious -- much like any competitive tennis player you'll encounter across the net. I can't imagine what the response (and odds) would be if I were casting, say, Transformers 3. Point is, it's impossible to get the part you're auditioning for all the time (or even most of the time) no matter how good, or "right" for the role, you are. So, to state the (perhaps) obvious and confirm what we've all suspected about "making it" in this industry: it boils down to being in the right place at the right time. How does this relate to tennis?
You give yourself the best shot of winning each point by always being in the right place at the right time to strike a ball. In a word: footwork.
In tennis, most of the balls you're going to hit are going to be no more than a few feet on either side of you. So when you're moving to the ball, you want to take little steps so that you remain balanced; are measured for your stroke; and able to easily change directions for your next shot, if necessary. To actors, I suggest the same thing. Keep making little adjustments/taking little steps toward your goal(s). Think of each class, or audition, or student film as a little step toward finding that role in your wheelhouse.
Sometimes in acting, in tennis, and in life, you have to take giant steps just to have a chance. But those usually wind up being desperation shots. The consistent player adjusts, and grows, and maintains his balance through little steps. And when you get in the habit of doing that, you'll find that you'll increasingly be in the right place at the right time.