One, when, we get the chance to use our skills to do useful and nice thingsOr putting it differently,
Two, when, we are forced to do useless stuff to learn useful skills
One, when we build our reputationOr putting it still differently,
Two, when we build our character
One, when we read and enjoy interesting writings
Two, when we struggle at memorising vague symbols by looking at relatively monotonous and ridiculously stupid books.