I couldnt agree more with this quote.
So many times we compare to others and think of ourselves as failures. They have achieved so much, yet we have achieved only so minimal.But have we truly looked inside for happiness? Instead we focused on other people's success till we forgot our own happiness.
To illustrate my understanding of this quote, in the context of getting an A grade for maths maybe:
Fufillment leads to achievement:
You grow to like maths, and hence you study more. Therefore through more practice this gives you an A.
Achievement leads to fufillment:
You think by achieving an A, you will be happy. So you force yourself to study, and be perfect in all your homework, tests, and exams.
See the difference?
As simple as it might sound, sometimes there might not be clear cut answers. For example, sometimes you might like maths but sometimes you might not. Then it will totally be a different story as you want to avoid the worst outcome and not fail maths exam, or sometimes it just boils down to responsibility on your part.
On a personal note, I'm really trying my best to strike a balance. Hopefully I will achieve through fufillment :)