Some people are vagarious, always changing their mind about things or making snap decisions based on whim instead of reason or sound judgment. You never know what to expect from a vagarious person!
Vagarious is an adjective related to the noun vagary, meaning "a random or unpredictable change." The root of both words is the Latin word vagari, meaning "wander." A person who wanders from a straightforward path is one who unexpectedly veers off on random side paths, ending up at destinations you couldn't foresee. It's the same way with someone who is vagarious in thought or behavior. Weather can be vagarious, too, and so can the economy. Both make planning difficult!