Theory:

     I am a very firm believer in one thing. You will ultimately become what your innermost and deep-rooted desire is. Of course, desires change for a person from time to time. But your deep rooted desire is what motivates you.
 
Which is the most important step in the goal setting process?
Explanation:
 
The author is a person who believes in one truth. In the long run, you will become whatever your inclination is. Most of the time, the person changes from time to time, depending on the desire. But your profound desire or whatever you are inspired of will make you achieve it.
  
The author asks, which is the most crucial step in the process of setting a goal?
 
Meanings of difficult words:
 
Numbers
Word
Meanings
1.
Believer A person who believes in the truth or existence of something.
2.
Desire Wish.
3.
Deep rooted Profound.
4.
Ultimately In the long run.
5.
Motivates Inspires.
Reference:
State Council of Educational Research and Training (2018). Term-1 English Standard-9. Goal Setting - Kris Srikkanth (pp. 127-130). Published by the Tamil Nadu Textbook and Educational Services Corporation.