Imagine this:
You are a traveler, and you've been walking amidst a mountainous path for days. The hot summer sun is blazing down upon you. Reserves of food are all but extinguished. You're exhausted, and you're experiencing a burning desire for rest and rejuvenation. 

Slowly wilting away as you walk, you turn a corner and see in the distance, plumes of white smoke drifting up and away. Although you can't actually see the source of the smoke, you're able to infer the existence of a man-made fire. Hope begins to fill you're heart. You know such a fire bring with it promise of people and much needed provisions. Without thinking twice, you set a course for the source of the smoke, and onward you walk. 

Guided by that distant signal, you eventually find way to a small village home to dozens of villagers. The villagers greet you with a smile and gladly give you food, water and a place to rest your head. Salvation is yours at last.

Within this story we can see what I'd like to call, the Inference Principle; which quite simply explains our ability to infer the existence of something without having any real, concrete evidence of that something. You see the smoke. You cannot see the fire, but you are still able to infer its existence.

This is one way with which we can come to know the Self.