capricious (part of speech: adjective)
transient (part of speech: adjective)
meteoric, shifting, temporary, sudden, transitory, instantaneous, fading, restless, temporal, brief, transient, mortal, rootless, momentary, ephemeral, short-lived, flickering, swift, passing, impermanent, mutable, vanishing, evanescent, cursory, short-term
motiveless (part of speech: adjective)
capricious, careless, reasonless, flighty, fickle, haphazard, ambivalent, indecisive, irregular, systemless, whimsical, motiveless, fanciful, sporadic, nonsystematic, flitting, wandering, chancy, rambling, spastic, unmethodical, volatile, wayward, random, adrift, impulsive, arbitrary
- The welfare and the happiness of my people alone lie on my heart- I think not of my own fleeting fame." - "Berlin and Sans-Souci", Louise Muhlbach.
- But another time, when I came down late at night to get a book from the library antechamber, and found her sitting in the hall- alone- the impression left upon me was the reverse of fleeting. - "The Damned", Algernon Blackwood.
- So the passing year had to take a fine brush and paint upon the small, wistful face a fleeting shadow, the mere ghost of a sadness that came and went as she watched and waited for the father love. - "In the Heart of a Fool", William Allen White.