Prayer has got very big effect in life. All will pray when they are in troubles. But only some prayers would be answered. Why? As per guru's declaration, the prayer should be warm and should be like a dialogue, with sincerity.
You should know what you are asking. If that is required at that time, that prayer would be positively answered. But, we should not be confident that once we prayed means, some one is ready in the sky to work for us. He is very selective and demanding. It is His world. He does what he likes for the sake of the world