Doctor brown shares his grandmother's theory with tita. what is the grandmother's theory?

Dr. Brown's grandmother believed that every person was born with a box of matches inside of them, but they were unable to strike the matches themselves. In order to light them, you need a candle and oxygen. The oxygen comes from people you love, the candle is things you enjoy like music, words, food, caresses and so on. These things combine together to light the match and for a bit we are dazzled by the dancing light. The warmth will grow inside each person and then it begins to fade slowly over time until a new something comes along to revive it. Every person has to find what it is that sets things things off and it nourishes each persons soul. If someone doesn't discover these things, the box of matches will get damp over time and no matches will ever be lit. In that case, the soul leaves the body and wanders in deep shade to find food to nourish itself, completely unaware the only the body it left can offer that food.