Purpose

If you can choose a purpose, a specific purpose, you have power over your life.   You can change minds.   You can change actions.   You can change perceptions.

However
1. What people want is never just one thing.   People want lots of things.   It is very hard to choose which one is the most important.   It is very hard to focus of one thing at a time.
2. Unless the purpose is very clear and specific, it is very hard to know what to do.

For example, if you want directions and your purpose is to go to "a good restaurant," it will be very hard to help you.
If you want directions to my friend John's house in Las Vegas, I can tell you exactly what you need to know.

When reading an assignment for a class, do you wish to be entertained?   Do you wish to be prepared for class discussion?  Do you wish to complete the homework assignment as quickly as possible?  Do you wish to kick ass on the test?

There is different advice for each option.