A man may not insist at different times on the truth of each of two conflicting allegations, according to the promptings of his private interest.

Explanation

(English-origin maxim.) A party who asserts one version of facts in one proceeding and a contradictory version in another is estopped — the law forbids blowing hot and cold to serve shifting private interests.

Where this applies

• A man tells one court he was in New York on the night in question to establish an alibi, then tells another court he was in Chicago that same night to claim a tax deduction — the law won't let him have it both ways.
• A woman claims in a personal-injury lawsuit that she's totally disabled, but in a separate insurance application she declares she's in perfect health — she's estopped from asserting whichever version suits the moment.
• A company tells regulators that a product is a "food supplement" to avoid drug-approval requirements, then tells customers it's a "medicine" to charge higher prices — the law forbids switching stories to serve shifting interests.