Do you fully understand the word "fully"?

Many Scientology publications include a directive like this:

"In studying Scientology be very certain you never go past a word you do not fully understand." (Sometimes, it's "very, very certain".)

Do you fully understand the word "fully" in this directive?

Here are some dictionary definitions:

• American Heritage Dictionary
• Cambridge International
• Dictionary.com
• InfoPlease
• Merriam-Webster Dictionary
• Webster's Online Dictionary

This leads me to a question.

Suppose you meet someone who knows nothing about Scientology - someone who's never heard of it before. Let's call this person "Jane". You lend Jane a copy of What Is Scientology?

Suppose Jane begins to read the book.

At what point does Jane fully understand the word "Scientology"?

How much of What Is Scientology? can Jane read before having to stop because she does not fully understand the word "Scientology"?

How does one come to fully understand a term that encompasses an enormous amount of information, history, and nuance, without going past a word that's not fully understood?