When a man reads a line or a paragraph in a copyrighted textbook that explains a fact T, and then he proceeds to wonder why T occurs, is asking a question (on Stack Exchange or another public forum) of such nature: "Why does T occur?" an infringement of copyright law? What if topic T was not very obscure?
In most copyright law (India is no exception), facts and ideas cannot be copyrighted. A particular expression of a fact or idea (i.e. the words used to say it) can be copyrighted, but not the underlying thought. The fact that I wrote this answer, for example, means I own the copyright to these particular words describing copyright law, but that certainly does not mean I own the copyright on the very idea of copyright law, and that no one may discuss copyright law without my approval.
Nuclear Hoagie's answer correctly notes that repeating the ideas and knowledge of facts is not copyright infringement when expressed in your own words.
Further, if you decide to include a short citation from a published book in your own text, that is normally covered by fair use or right to quote rules in the copyright law. In most countries, it is enough if the citation is short in length compared to the whole work, and it is directly related to your own work. In every case it is necessary to credit the original author of the citation.
I'm not familiar with India's copyright law in particular, but this seems to fall under the "criticism or review" and "personal use" categories in Exceptions To Infringement Under Copyright Act, 1957.