Why was it require that he who alleges fraud or mistake in entering contract must prove allegation?

In legal contexts, the principle that the party alleging fraud or mistake must prove their claim is rooted in the foundational concept of burden of proof. This requirement ensures that allegations are substantiated with evidence, maintaining the integrity of contractual agreements. It prevents frivolous claims that could undermine the reliability of contracts, which are essential for trust and predictability in transactions. By placing the burden on the alleging party, the legal system seeks to uphold fairness and protect against unjust outcomes.