BAILING ON A PROMISE / YOUR WORD / AGREEMENT / CONTRACT
Don't do it.
An agreement made by an actor to a director or producer to perform in a production is a CONTRACT. Period. IT DOESN'T HAVE TO BE IN WRITING. A legal contract consists of an OFFER and an ACCEPTANCE. So long as there is an OFFER of a role (made by the producer or director) and an ACCEPTANCE of a role (made by the actor), a contract has been made, and is legally binding and enforceable.
Your word (oral contract), your handshake (an obvious agreement / contract), your informal agreement in an email, or your formal signature (written contract), is GOLDEN.
GUARANTEED: if you bail on a theatre or a film or video project, or go back on your word to a director or a producer, it will be reported by the theatre / producer / director to other theatres, filmmakers, producers, directors, and occasionally to critics. And those in a hiring position will soon learn that you are not to be trusted.
You may feel you're getting away with it in the short term, BUT ... it WILL get around to other directors and producers, and critics in due time ... critics in theatre, in film, in TV, in radio, in newspapers, etc. Producers and directors talk to each other -- as well as to critics -- just like actors talk to one another. And we phone each other to ask what our experiences were with the actor. And we talk to critics. Recall that audition you went on where you weren't invited back to a call-back, or when you weren't cast after you gave that great audition, or when you weren't called in for a role you thought you were PERFECT for?
Unless you're a total screw-up on set or during rehearsals, we won't replace YOU if we find someone better than you after we cast you. Don't do it to US.
If -- for only 2 rare but EMERGENT reasons beyond your control: a day job transfer out of state, or a severe and prolonged illness requiring your immediate hospitalization -- you have to ask to be released from your contract or an oral commitment that you made, DON'T DO IT VIA EMAIL OR
VOICE MAIL.
Communicating with a director or producer like this shows nothing but cowardice on the actor's part, along with the prospect that in all probability you're lying. Show that you have backbone and decency, and do the right thing: meet in person with the individual who hired or who cast you, face them, and explain your circumstance. If it's utterly impossible for a face-to-face meeting (i.e., if you're living on opposite ends of the country), then at the VERY least, phone them and speak with them DIRECTLY (absolutely no cowardly voice mail messages or messages left with whoever answers the phone, etc.). You weren't hired or cast via an email; don't QUIT via an email.
The fact that you received a better offer or a larger role in another film or production, or you don't get along with one of the other actors, or you don't like the director, or you don't feel you're doing well in the role (let the director decide that ... not you), or you lost your day job, etc., is not sufficient reason to break your promise or your commitment and leave the entire production company in a lurch and threaten the continuity of the production.
Other casting decisions may have been made based upon your commitment to the project.
Costumes were made or purchased to your measurements.
Press releases were written and sent to the press and to critics with your name on them.
In addition to the above, bailing on your word is morally and ethically wrong. It's a terrible way to treat people who placed their trust in you. And it's unprofessional.
You made a promise to someone. Be a man / woman of your word. If you say you're going to do something for someone, follow through and do it.