If somebody is not willing to share the knowledge, it is foolish. If there is a well. Somebody should take water regularly from the well. Then only the well be giving fresh water. Otherwise the well will become a waste.
So as told by author every one should share whatever knowledge he had should see that somebody else will get benefited. Hence my sincere request to all learned people to be kind enough to share the subject with the people who require some knowledge.
A positive attitude will lead to positive results.
But participating or addressing a uniform audience or forum of a particular commonality this should not be so. There you have to orient and adapt yourselves to that level where the audience and you can meet and they get to gain from your expertise or entertaining.