Does expecting bad things to happen to oneself make them happen, and what is the religious ruling on optimism for oneself, and do some of them happen without others, or is Allah more merciful to His servant so He does not let them happen, and what should someone do if sadness is constant for them and they expect nothing but bad things?

A person should refrain from speaking about the evil they anticipate for themselves, because doing so might harm them. This is exemplified by the Bedouin whom the Prophet, peace and blessings be upon him, visited, and who wished for death upon himself, and the Prophet agreed with him. Similarly, a person should be optimistic and rely on Allah, because pessimism is a bad opinion of Allah and can lead to the actualization of evil, whereas optimism and trust in Allah repel evil. Divination (pessimism) is polytheism (shirk) and a bad opinion of Allah, making the pessimist vulnerable to affliction. And whoever fears anything other than Allah, Allah will subjugate him to it. However, this applies specifically to pessimism and a bad opinion of Allah, and not everything a person divines will necessarily occur, for the matter depends on Allah's will and decree.