  The Mean Field Approximation (MFA), or continuum method, is often used in
courses on Networks to derive the degree distribution of preferential
attachment networks. This method is simple and the outcome is close to the
correct answer. However, this paper shows that the method is flawed in several
aspects, leading to unresolvable contradictions. More importantly, the MFA is
not explicitly derived from a mathematical model. An analysis of the implied
model shows that it makes an approximation which is far from the truth and
another one which can not be motivated in general. The success of the MFA for
preferential attachment networks is therefore accidental and the method is not
suitable for teaching undergraduates.
