Our expectation of the gratitude of others for what we've done for them is sometimes exaggerated because of our deep desire for appreciation and approval. When our good work or good deeds go unrewarded by hoped for praise, we feel like failures so we treat those who denied us our due as betrayers.
It follows that the word probability, in its mathematical acceptance, has reference to the state of our knowledge of the circumstances under which an event may happen or fail. With the degree of information we possess concerning the circumstances of an event, the reason we have to think that it will occur, or, to use a single term, our expectation of it will vary. Probability is the expectation founded upon partial knowledge.