Qarun came from Musa's own people and had wealth on a scale the Quran describes through a strange, brilliant detail: the keys to his treasuries were a burden for a group of strong men to carry (28:76). Just the keys. His own community, not enemies, gave him sincere advice: do not exult, seek the home of the Hereafter with what Allah has given you, do not forget your share of this world, do good as Allah has done good to you, and do not seek corruption (28:77). Reasonable, warm, and completely rejected.
His reply is the most quoted self-made-man line in scripture: “I was given all this on account of knowledge I possess.” (28:78). He went out before his people in his full splendour, and those who wanted worldly life sighed that they wished they had his luck. Then the earth opened and swallowed him and his house, and there was no faction on earth to help him, and he could not help himself (28:81). The next morning the same people who had envied him were saying, without irony, that it is Allah who extends provision and restricts it.