The Reason Behind Forgetting Quran

It is reported that Al-Ḍaḥḥāk b. Muzāḥim, the famous scholar of tafsīr from the Tābiʿīn, said:

No one who has learned Qurān and then forgotten it except due to a sin he has committed, because Allāh the most high said: وَمَآ أَصَـٰبَكُم مِّن مُّصِيبَةٍ فَبِمَا كَسَبَتْ أَيْدِيكُمْ Qurān 42:30 “And no calamity befalls you except due to what your own hands have earnt.” And forgetting the Qurān is one of the greatest calamities.

Qurān 42:30