犬も歩けば棒にあたる
Inu mo Aruke ba Bou ni Ataru
This idiom has a double meaning. The negative connotation is that showing off, or acting on impulse (like a dog walking off on its own), can lead to misfortune (like getting hit by a stick). A broader negative meaning can also be that bad things just happen in life. The positive meaning is that "As long as you keep on going on, something good will happen" (like a dog who happens to find a stick).