Actions speak louder than words but if the person cannot see your actions then they must try and believe what you say until they can see your actions.
if you promise something people might not actually believe you until they see you actually do it.
it means that what you do shows how you really are. you can say one thing, but it doesn't prove that you mean it. Therefore the way you act shows a lot about your character.
actes sont plus éloquents que les mots
Actions speak louder than words means that what you do is more significant than what you say.