Why do people have unprotected sex during an affair?

I can't figure this one out. Why do people have unprotected sex during affairs? (mainly women) If you are a WS, what was going through your head? do you know why? I'm not judging anybody I just want insight. I can't understand why normally very careful people would put themselves at risk like that along with their partners. It seems to be a well documented phenomenon that people are much more unsafe in affairs, but I've been looking online for 'why' and can't find a thing. I am looking for real answers as to the psychology behind why - not 'she's an evil uncaring b****' I would like to hear from WS if they can pinpoint why they did it, or BS if they have theories.

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