De Bono points out “one of the major limitation of [traditional] judgement system of thinking is that it is REACTIVE rather than PRO-ACTIVE. This means that you criticise ideas rather than create them."

Criticise = pass judgement = evaluate = analyse = play devil's advocate = black hat thinking.... these should be reserved for the evaluation stage, and avoided as much as possible during the ideas-generation phase. We all do it. And we could all benefit from refraining.

From the GM Design Blog.