The most common mistake in a personal statement is not bad writing. It is writing that could have been written by anybody.
A statement that opens with a passion for helping people, a lifelong fascination with science, or a quotation from a famous figure tells the reader nothing they cannot get from ten thousand other applications that year.
What works is specificity. A moment. A problem the student actually tried to solve. What they got wrong the first time. What changed in how they think because of it.
This is why we do not hand students a template at our retreats. They draft, they read it aloud to peers, they get it pulled apart, and they rewrite it before they leave. A drafted and critiqued statement is worth more than a workshop on how to write one.

