People who are just getting into the acting business have quite a few misconceptions about how the casting process works. The best way to illustrate this is with a hypothetical example giving a fictional show. Let's say the producers of a daytime soap called "Sullivan Street" have just gotten a script for one of next month's episodes. In this episode there is a new character by the name of "Tara." She is a real schemer who is going to seduce the show's star.
The first thing the producers do is call the casting director they have used for many years and describe the character, Tara, to him. Immediately the casting director will already have several people in mind who he has worked with in the past but he will still submit a description to Breakdown Services. This is a company that serves as a link between casting directors and agents. The next morning all the agents read the "breakdown" sheets to see what parts are being cast. The agent will then look through his files to see if he has anyone who fits the description. He'll select several photos and send them to the casting director. The casting director then receives all these envelopes from all these agents, and there are tons of them. A casting director will have to go through hundreds, maybe even thousands of photos looking for "Tara." And then even if the photo looks great the casting director will look at the attached resume to see what body of work the actress has done. Finally the casting director will narrow these hundreds of photos down to about 30 or so and will call these agents up for auditions.
The agents will then call their clients up and tell them about the audition, the time and place. He may send them sample scripts or have them come to his office to pick them up. After this the actress goes to the audition, probably nervous as heck. She'll dress up the way she thinks Tara should dress. She wants to get the character just right. While waiting for her audition she takes the time to go over her lines. Finally, she makes it into the casting director's office and does her reading for the part. She does well, but is not too hopeful since she has had other readings during the week for other parts that she didn't get. After the audition is over the goes home and waits. In a day or so she gets a call from her agent that they liked her audition and they want her to come back for a second one. She's all excited. She goes back for a second audition, reads the same part again and does even better than the first time. She is positive that she is going to get the part. Then, at the last minute, the producers, who are at the second audition, decide that Tara should be a blonde instead of a brunette. Yes, that is the way it goes. Sometimes you'll lose a part because you are the wrong height or hair color or something really stupid. Then a month later they'll call you back in to read for the starring role of a new series they're putting together. That is the way careers are made and broken in this business and there is just no logical reason to the madness. All you can do is go with the flow and hope for the best.