Conventional/received wisdom noun phrase
General knowledge is accepted by the public.
The received wisdom has it that give a man a fish and you feed him for a day, but teach a man to fish and he'll eat forever.
The conventional wisdom is that if the dragonfly flies high it will be sunny, and if it flies low there will be rain.
The expression is often recorded to the economist John Kenneth Galbraith, who used it in his book The Affluent Society in 1958.
To do domething based on your emotions rather than for rational reasons
I can't believe that Tom beat his classmate. He's always the one who let his heart rule his head.