The optimization principle, Delta T/T = const, was wrongly shown to hold for balanced counter-flow heat exchangers due to an inappropriate analogy between a balanced counter-flow heat exchanger and a one-dimensional thermal insulation system in a paper entitled "A general variational principle for thermal insulation system design" by Bejan and then in his subsequent papers. The heat exchanger effectiveness of a balanced counter-flow heat exchanger is well known to be highest where the local temperature difference between the hot and cold streams is uniform along the entire length, with this principle Delta T= const, being independent of the absolute temperatures of the streams as the uniformity principle of the temperature difference field indicates. That is, the optimization principle for heat exchangers with the purpose of heating objects is Delta T= const, rather than Delta T/T = const. Hence, Bejan's accusation that the uniformity principle of the temperature difference field is a duplication of his optimization principle, Delta T/T = const, for the one-dimensional thermal insulation system, is unfounded. These principles should not be confused since they apply to different scenarios. (C) 2018 Published by Elsevier Ltd.