Stabilization of ferroelectric negative capacitance (NC) in a transistor gate stack is a promising pathway towards future low power electronics. However, most modeling efforts of such NCFETs are based on single-domain Landau theory, which is an oversimplification that leads to incorrect predictions and device design. By extending the Landau model to describe more than one domain, it is shown how an internal metal electrode inherently destabilizes NC. Consequently, NCFETs have to be designed without internal metal electrode to function. Furthermore, the use of single-domain Landau theory to model NCFETs with HfO2 based ferroelectrics is critically discussed.