Originally posted by jgredline Can you please explain?
The metering system isn't omniscient. It tries to guess how to best pick one single exposure value for the whole scene. If it (due to meter zone alignment or other arcane workings of the matrix-metering mode, or if you're using spot metering and point right ad it) picks something very dark as the basis for that exposure, the rest of the scene will be overexposed.
Generally matrix-metering is very smart, but I often prefer predictable over smart and go with center-weighted instead -- dialing in my own EV compensation where appropriate.