My "cure" is linked to your "cure"

Today Sachin introduced me to metaphysical meditation, where he gave me a thought :
"In helping others to succeed, I shall find my own prosperity. In the welfare of others, I shall fnd my own well being" by Sri Sri Paramahansa Yogananda
to ponder upon and think why this saint said such a thing ? Do I really believe it is true? and also explain my answer.Initially, it was really difficult to focus only on this thought when sometimes I got distracted by various sounds (rains, chirping of birds etc..) and my own various unwanted thoughts. I thought that it is true only in some cases. A gave an example to support that too. One of my friend used to spend so much time helping others before every exam that he never had time to prepare for his own and so used to score less.So, you can say that he never found prosperity in helping others to succeed. But the flaw with this argument is that we are linking prosperity just to a result of a few exams and seeing this in a very narrow context. Actually if you see his present situation, he is doing something which he likes and has become an expert in his domain in a very short time. Now the question arises why is this so? It like if you throw a stone in a pond, the waves will originate from that point and come back and terminate at the same point where they started. This analogy is true for the waves of our good work also, which will come back to us. Also at metaphysical level all of us are part of just one atma (soul).
Also another explanation for this would be that when a person works selflessly for others, he is putting in some efforts, which makes him strong (both mental and physical) and knowledgeable and when the time comes to work for himself, only a little effort will bring great results due to his experience and strength.
Now the question is: why am I sharing all this with you? It is because I want to tell you that as a person who stammer (PWS) if we work for other's cure, we get cured indirectly. Which I have observed in my own case. So we should try really hard, until helping others without any expectations becomes a part of our natural self. This will give you immense joy and pleasure.