Additive ideas come to mind quickly and easily, but subtractive ideas require more cognitive effort. Because people are often moving fast and working with the first ideas that come to mind, they end up accepting additive solutions without considering subtraction at all.

we need to go from thinking add  or  subtract to thinking add  and  subtract. The add  or  subtract framing forces us to try and resolve an apparent contradiction. If A is true, then not-A must be false. If I like subtracting, then I must not like adding. Resolving contradiction is not a bad thing. Doing so has aided reasoning at least since Aristo

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