To predict something is foretell it, often but not always with precision of calculation, knowledge, or shrewd inference from facts or experience. To augur something is to divine or predict it, as from omens. Augur also means to bode, as in the case of a consumer trend that augurs well for a company. Augur is easy enough to find in contemporary writing and speech, but it is rooted in ancient mysteries: the noun augur, which predates the verb in English, refers to one of a group of Roman officials charged with observing and interpreting omens for guidance in public affairs.
The word disappointment refers to a feeling of being let down, or to something that produces that feeling by failing to fulfill expectations or wishes. The noun chagrin is more pointed: this word refers to a feeling of vexation or irritation marked by disappointment or humiliation—or both!
The word changeable can mean simply capable of being changed or, more often, liable or likely to change. Mercurial is closer to the latter; it emphasizes volatility, fickleness, and unpredictability, and is commonly used to describe person’s temperament. But even the meaning of mercurial shifts from time to time; this hard-to-pin-down adjective can also take a more positive turn to mean animated, lively, or quick-witted.