Do people actually do bad things for "selfish reasons" or is that just a made up idea of everyday people that don't know about human psychology?

I'm not talking about bad things in the sense of illegal things, rather things we deem to be negative or unethical on a personal level. For example, cheating on someone, stealing, being mean, etc. <br><br>Does it sort of make sense that humans do things for positive reasons? For example, someone is cheating on their partner not because they want to be malicious, deceitful, manipulative and selfish, but because they don't know how to end the relationship and don't want to hurt them, they want company, they're afraid of being alone, they want to feel wanted and desired and appreciated by someone else. <br><br>That's a very basic example, but everything out of the ordinary we do that's seemingly unethical or negative to others, is it really for positive reasons on a deep psychological level?