When we socialize around, we make friends. So we have friends every where around us. Initially we may feel that all friends are good friends and they are all precious.
As time passes we see that our friends change in their personality, in their goals, in their life style etc. As time passes people develop selfishness and would like to develop themselves. So friends will turn more selfish towards themselves and may not help their old friends. Some times friends may see that they gain more if their friends lose or go down in life. So they may not remain good friends for long.
After some time we realize there are very few friends that will remain with us in all conditions of our success, failure, happiness, sadness. There will be very few friends who can help us, sacrificing some time, effort, and gains of themselves. Those are the true friends. Some timely help from the true friends gives a lot of push for us in terms of confidence.
Thus we find that true friends are rare and precious like diamonds and false friends are like leaves lying everywhere.