Through examples, you should demonstrate your desire to enter a particular field of study and attend a particular institution. Avoid using grandiose adjectives in describing yourself and be sure to admit your weaknesses. The essays should demonstrate intellectual curiosity. Sometimes a relaxed conversation about your background, rather than a formal statement, can be the best approach. They want to read about what has happened in your life and how it has made you special.
Essays based on a challenging experience generally stick in the minds of admissions officers.
It was an explanation for leaving a job. It's an example of someone answering the question of what was the most challenging thing that happened on the job. If she hadn't answered with that, she wouldn't have been honest, and she wouldn't have given us the insight she did. Many students try to distinguish themselves with creative or unusual approaches to their essays. I've also gotten audio- and videotapes.