Why does the element Iron have a variable valency, sometimes Fe+2 and sometimes Fe+3?

Iron, as a transition metal, shares the same outer electronic configuration as the rest of the metals in its class, meaning the 4s orbitals are all the same.  Only the inner 3d orbitals change among these metals. However, these orbitals (4s and 3d) are close in energy, so sometimes Iron gives up its 2 outer 4s electrons, and sometimes it also gives up an inner 3d electron, resulting in an Iron ion having either 2 or 3 positive charges (Fe++ or Fe+++)