This is to reflect the shortness of the worldly life. Allah (swt) says:

  ﴾قَالَ كَمْ لَبِثْتُمْ فِي الأَرْضِ عَدَدَ سِنِين % قَالُوا لَبِثْنَا يَوْمًا أَوْ بَعْضَ يَوْمٍ فَاسْأَل الْعَادِّين﴿

(He (Allah) will say: “What number of years did you stay on earth?” % They will say: “We stayed a day or part of a day. Ask of those who keep account.”) (Al-Mu’minun: 112-113)

Let us end this Surah by this example: If you ask any person whose age has reached sixty, seventy or eighty: How have these sixty years of your age been? He will say: It feels as if they were only a short moment! An afternoon or a morning.