A truth isn’t only that which is in accordance with fact, but also that which is aligned with universal laws and the nature of experience. At the worldly level, there are three kinds of universal laws for which human beings must abide or feel the unpleasant consequences: physical laws, psychological laws and moral laws. Very early in life, we all learn that we must obey the laws of gravity because falling and getting scraped knees is painful. We also quickly learn that putting a hand in fire burns. Both gravity and fire are just a few of the physical laws that we must abide by in order to avoid feeling pain. Another physical law is the law of change. Each of us is eventually going to grow old, sick and die. There’s nothing that can be done about this. As much as we’d wish it were different, in this world of opposites you can’t have a universe without both creation and destruction (death).
We also have psychological laws that govern us, so that sorrow, fear and anger will always feel bad, and security, peace and happiness will always feel good. We know that certain actions cause psychological damage—mostly by being on the giving or receiving end of abuse and injustice—and so we try to avoid them or seek help when exposed.
Lastly, there are moral laws that generally keep us from causing harm to others—usually in the form of lying, stealing or killing. Moral laws are, in essence, The Golden Rule—“Do unto others as you would have them do unto you.” As intelligent beings, not only do we avoid doing harm to others out of empathy, but we also avoid doing harm in order to protect ourselves from any possible retribution. So, in a sense, “Do no harm” is a truth that helps protect ourselves and others.
To summarize, rub against God and God rubs right back. There is no negotiating. Even if you get away with it today, you won’t tomorrow (the law of karma). So it helps to know the rules of the game if a relatively peaceful life is what you want.
On the other hand, a lot has been written about what distinguishes the truth from non-truth. In the West, such discussions mostly end up being circular as philosophy attempts to perform a form of intellectual gymnastics. But the answer isn’t as complicated as it seems. Ultimately, the truth is that which cannot be negated. It’s that which, when thrown into a red-hot furnace with all other objects, relationships, ideas, concepts and beliefs, still remains.
In the Bhagavad Gita it is stated:
Weapons do not slay it, nor does fire burn it. Water does not drown it, nor does wind dry it. It cannot be slain, burnt, drowned, or dried. It is changeless, all-pervading, stable, immovable and eternal. (2.23–24)
The one truth that can never be slain, burnt, drowned, or dried is the truth “I am.”
Upon analysis, you can negate everything else but you cannot negate the fact that you are having an experience—even if that experience is the experience of “nothingness.” The only question then, is what is this “I” that is experiencing? What is this one real truth that which all other truths rest on?