They go on suffering and yet hold on in memory the very source of suffering. Memory must be one's obedient servant; when it is a master then life becomes difficult. A person who cannot throw away from his memory what he does not desire to keep in mind is like a person who has a safe, but the key of that safe he has lost. He can put in money, but he cannot take it out. All faculties in man become invaluable when a person is able to use them at will, but when the faculties use the person, then he is no longer master of himself.