(a.) Incapable of being foreseen.

accidental adventitious agnostic aleatory ambiguous capricious casual causeless chance chancy changeable contingent destinal dicey doubting equivocal erratic extraordinary fatal fatidic fickle fluky fortuitous hesitant hesitating iffy improbable incalculable incidental indecisive indemonstrable indeterminate irresolute more than expected out-of-the-way past expectation polysemous risky skeptical sudden touch-and-go unaccountable unannounced unanticipated uncaused uncertain unconfirmable unconvinced undetermined undivinable undivined unexpected unforeseen unguessed unheralded unhoped for unlooked-for unpersuaded unpredictable unpredicted unprepared for unprovable unsure unverifiable variable wavering whimsical without warning