What should I write in the introduction of my personal statement?

Whatever you do, do not start with a quote - that is personal statement 101. It's better to start off with a simple statment of why you want to do the course you are applying to.

For example: "I am applying to study a BA in Experimental Psychology because studying psychology at A-Level nurtured my intrigue in the relationship between the mind and behaviour."

Remember that the admissions tutores are interested in why you want to study the course and not how you came to that conclusion. So avoid long descriptive tales of how you decided on the course and get straight to the point.