How we perceive earth, and those that people it, influences how we pray and often what we pray for. A positive worldview feeds prayer with a healthy, progressive expectation of good. Whereas, a negative worldview can tend to leave one feeling cornered by problems and can sink prayer in a sea of hopelessness.
The truism, "One rotten apple spoils the barrel," is a good reminder to watch the influences you let in. But I think that, as it it relates to prayer, the apple or influence that we need to be most concerned with is our own! I remember a friend sharing her take on apple theory. She said, "You can't be a good apple in a barrel of rotten apples!" This always reminds me that if I see myself as an isolated island of good in an evil world, I am sunk - and so are my prayers.