Because the end (telos) is the principle of every change, and potentiality exists for the sake of the end, actuality, accordingly, is the end.
bɪkˈʌz ðɪ ˈɛnd tˈiːloʊz ɪz ðə pɹˈɪnsɪpəl ʌv ˈɛvɹi tʃˈeɪndʒ, ænd pətˈɛnʃɪˈælᵻɾi ɛɡzˈɪsts fɚðə sˈeɪk ʌvðɪ ˈɛnd, ˌæktʃuːˈælᵻɾi, ɐkˈoːɹdɪŋli, ɪz ðɪ ˈɛnd.