Believe

In my life, I have seen many people with different views about life, after life, God and etc. Some think they believe, Some fake it and some deny it and some really truly believe. Last night I was at the mourning of one of my friend's grandmother and I heard the following conversation.

-X is very depressed. I don't know what she can do to get better.

-Why don't she start believing (in God)?

This made me think, does believing to any thing, can me us survive certain situations? Also how can we determine how much believe is required for making things happen?I have heard stories of miracles and what happened to that end. But it always is a big question mark in my mind; How much strength/beilieve/focous is enough? And how much is too much, that will confront others belief?