It means that it may be one way or another, there are too many factors that affect it. You say so, if you do not want to say yes or no. Sometimes it's a phrase to evade a direct answer.

Maybe - yes. Maybe - no. It (my decision/answer) all depends on other factors which I have not yet thought about, or factors which I don't know. As Nadine wrote, it is often used as a way to avoid giving a definite answer - usually to avoid giving a definite "No". Frequently, it means: "probably not/no......unless you can convince me."

The saying means the global wisdom of mankind. It depends - if your wish is to be fulfilled it is to be coordinated and planned with the billlions of other people's wishes for it to come true, let alone your wishes that change every day. Only strong wishes come true in this ocean of wishes, but this law works everywhere on the planet.