Armstrong was supposed to immediately shut the engine down, as the engineers suspected the pressure caused by the engine's own exhaust reflecting off the lunar surface could make it explode, but he forgot.
ˈɑːɹmstɹɔŋ wʌz səpˈoʊzd tʊ ɪmˈiːdɪətli ʃˈʌt ðɪ ˈɛndʒɪn dˈaʊn, æz ðɪ ˌɛndʒɪnˈɪɹz səspˈɛktᵻd ðə pɹˈɛʃɚ kˈɔːzd baɪ ðɪ ˈɛndʒɪnz ˈoʊn ɛɡzˈɔːst ɹᵻflˈɛktɪŋ ˈɔf ðə lˈuːnɚ sˈɜːfɪs kʊd mˌeɪk ɪɾ ɛksplˈoʊd, bˌʌt hiː fɚɡˈɑːt.