Doctor Brown shares his grandmothers theory with tita. What i sthe grandmothers theory?

From the text:

My grandmother had a very interesting theory; she said that each of us is born with a box of matches inside us but we can't strike them all by ourselves; just as in the experiment, we need oxygen and a candle to help. In this case, the oxygen, for example, would come from the breath of the person you love; the candle could be any kind of food, music, caress, word, or sound that engenders the explosion that lights one of the matches. For a moment we are dazzled by an intense emotion. A pleasant warmth grows within us, fading slowly as time goes by, until a new explosion comes along to revive it. Each person has to discover what will set off those explosions in order to live, since the combustion that occurs when one of them is ignited is what nourishes the soul. That fire, in short, is its food.

If one doesn't find out in time what will set off these explosions, the box of matches dampens, and not a single match will ever be lighted.

"If that happens, the soul flees from the body and goes to wander among the deepest shades, trying in vain to find food to nourish itself, unaware that only the body it left behind, cold and defenseless, is capable of providing that food."