Forced collectivisation of an entirely agrarian economy.

Industrial policy that encouraged small scale iron smelting in homemade furnaces causing huge environmental damage.

Agricultural policy that ordered the extermination of sparrows who then couldn't keep insect populations down causing catastrophic damage to crops.

Brutally cracked down on any dissenting voices, including scientists who happened to point out the potential flaws in Maos plan

Contrary to OPs post, covering up the mistakes afterward and blaming outside influences and counter-revolutionaries rather than the failure of central policy.