Pothos cutting stems have only a single growing tip at the end and when that dies, then that is generally the end of it. I agree with what Alyssa has said about the difficulty in making the transition from water to soil.
I would add that a single stem cutting will never make for much of a plant because at best it will always be just a single stem that just grows longer and never branches or pushes out new stems from the soil. Therefore, it is best to propagate a half dozen or more stem cuttings and pot them together.
