There are two quite distinct classes of thoughts your thoughts think about:
1: Thoughts about things that are actually significant to your existence, (always things that have a physical reality).
2: Thoughts about things which, perhaps entertaining and things which the rest of the world says are real and significant, to life clearly are not.
To discover, see, realize this individually for yourself spells the conclusion to every question, complaint and uncertainty you have ever had, and makes your mental eyes suddenly focus in a manner you never knew existed.
To get started, (if you have the interest…which at least suggests you may have the ultimate ability), all you need do is privately look into this matter in your own head, and with scientific… oh to hell with, “scientific,” how about simply, “intelligent” scrutiny.
Allow the obvious reality of the situation to register in you. The plain fact that some, (if not most), of the things your thoughts think about do not exist and have no importance to your life.
The experience called Enlightenment is nothing other than understanding this, but as simple as it be, when you have it, you then recognize that of the next billion people you pass on the street, you are the only one who does.
J.