Does the pessimism or optimism of some people upon hearing a sound in the ear or experiencing an eyelid twitch have any basis in Islamic law?

There is no basis for pessimism stemming from ṭiyarah (omen-taking), and the Prophet ﷺ abolished it, informing us that it is polytheism (shirk (definition)). A Muslim must rely on Allah and ward off pessimism by proceeding with his affairs, and should supplicate: "O Allah, none brings good deeds except You, and none wards off evil deeds except You, and there is no might or power except with You." As for fa'l (optimistic augury), it is good and pleased the Prophet ﷺ, and it is a good presumption concerning Allah.