You can easily get "invalid" circuits when using diodes (the standard assumption of 0.6V or 0.7V drop across didn't make sense). I once got one of those on a fi

You can easily get "invalid" circuits when using diodes (the standard assumption of 0.6V or 0.7V drop across didn't make sense). I once got one of those on a final exam and waster 40+ minutes trying to figure out why my solution was "impossible." The teacher later cancelled that question, but I didn't get my 40 minutes back. Many lesson learned: A) don't be stubborn, let go; and B) circuit models ≠ circuit reality.