Have you heard of the saying 'ignorance is bliss'? There is a school of thought that more intelligent people are less happy than less intelligent ones because they are always worrying and thinking about the consequences of things, and the fact that often they are impotent to change things that they see wrong are wrong with the world. Whereas a less intelligent person will not understand these things and consequently does not have to think and worry about them, and may be happier as a result. I believe that is what the sentence is trying to express. 'Grief' has two connotations. its quite a clever word to use. The first connotation is tremendous sadness, for example when a person dies. The second connotation is that of being troublesome, for example if someone or something is bothering you, you can say 'stop giving me grief' or this is 'giving me grief.' So y increasing your knowledge, you may increase both your sadness, and also increase the amount of problems that you have to deal with.

I think that it means the one who knows much about every thing around him, keep looking for the reality and the truth behind everything, he becomes very deeply involved in things he never knew and so he becomes very smart and deeply intelligent and reaches wisdom but at the same time this may bring him sorrow, pain or grief as mentioned because he becomes aware of things people may not be able to accept or even appreciate. Maybe he was happier and was able to live without responsibility or paying much attention to everything. I wish this could help you.