I think that congratulations to some people is a good thing because they will know that we are happy with them, and they will feel proud of themselves, as, for example, I once received a congratulation.
I think congratulations on some great things. Because they will know that I am happy with them. And they do not feel proud of myself, like I once was congratulated.
I thought congratulations to someone is a good thing. Because they know we are happy with them. And they can feel proud of myself as well as I once received the congratulations!