A memory occurs when stimuli such as sights or sounds are so complex that the nervous system cannot receive all the impressions at once.
ɐ mˈɛmɚɹi əkˈɜːz wɛn stˈɪmjʊlˌaɪ sˈʌtʃ ɐz sˈaɪts ɔːɹ sˈaʊndz ɑːɹ sˌoʊ kˈɑːmplɛks ðætðə nˈɜːvəs sˈɪstəm kænˈɑːt ɹᵻsˈiːv ˈɔːl ðɪ ɪmpɹˈɛʃənz ɐtwˈʌns.