Wishful thinking is the formation of beliefs

Wishful thinking is the formation of beliefs and making decisions according to what might be pleasing to imagine instead of by appealing to evidence or rationality.
Studies have consistently shown that holding all else equal, subjects will predict positive outcomes to be more likely than negative outcomes. See positive outcome bias.
Prominent Examples of Wishful Thinking Include:
Economist Irving Fisher said that "stock prices have reached what looks like a permanently high plateau" a few weeks before Stock Market Crash of 1929, which was followed by the Great Depression.

British Prime Minister Neville Chamberlain informed the public that the 1938 Munich Agreement guaranteed "peace in our time".

Operation Barbarossa, Hitler's plan for the invasion of the Soviet Union.
President John F. Kennedy believed that, if overpowered by Cuban forces, the CIA-backed rebels could "escape destruction by melting into the countryside" in the Bay of Pigs Invasion.