口は災いの元 (くちはわざわいのもと): words can lead to disaster; the tongue is the root of calamities; the more you open your mouth the more likely you are to put your foot in it

words can lead to disaster; the tongue is the root of calamities; the more you open your mouth the more likely you are to put your foot in it

A warning that the mouth is where trouble starts. Said just before, or just after, someone says too much.

A Japanese proverb (ことわざ)