Binary thinking is when a person assumes that the situation can be broken into only two options. You either stop or go. You’re with us or against us. You’re loyal or disloyal. You’re us or them. Fight or flight.
It’s pretty rare that a situation is actually a binary, although there are times. But, in general, when people make bad decisions it’s because they thought it was a binary situation and it wasn’t.
For instance, imagine that you’re trying to get somewhere, and your normal route has terrible traffic. If you say, “Maybe this route isn’t working,” and the other person in the car says, “Oh, so you’re saying we should just go home,” they’re engaged in binary thinking. Or imagine that you’re trying fix a lawn mower, and what you’re doing just isn’t working, and you say, “This method isn’t working,” and the other person says, “So, you’re saying we should just give up.”
Humans are comfortable with binaries,[1] and so skeezy salespeople will always try to get you to reduce your choices to a binary. The fundamental binary is us or them.
Sometimes people think they aren’t engaged in binary thinking because they think there is a continuum between the two extremes. But, that’s still deeply fallacious, in that it’s rare that there are two options between which one must choose, especially in politics (there is not a continuum of furthest “left” to furthest “right”–political affiliations, at least as far as policy, are more usefully described in matrices), and the continuum model makes the situation a zero-sum. If there is a binary between black and white, then the more black something is, the less white it is. The less white something is, the more black it must be. Binary thinking contributes to zero-sum thinking, in which people approach a situation as though any gain for them is a loss for us. While business discourse long ago abandoned that way of thinking, it’s heavily promoted by tribal media.
[1] The research on the attractions and fallacies of binary thinking are usefully summarized in Mistakes Were Made, Superforecasting, and Thinking, Fast and Slow.