Vagary

 
A vagary is an unexpected and inexplicable change in something (in a situation or a person's behaviour, etc.); an erratic notion or action; an impulsive or illogical desire; a caprice. It tends to be used more in the plural - vagaries - than the singular. For example "the vagaries of the weather"; "his wealth fluctuates with the vagaries of the stock market"; "he has dealt with human vagaries for many years" .