I told my husband I left my previous job because I wanted better opportunities. The real reason was that my manager constantly made me feel incompetent. Nothing dramatic happened, and there was no single incident I could point to. I just slowly stopped recognizing myself.
I didn't tell my husband because he admired how "strong" I was and I felt ashamed that another person's words had affected me so deeply. The new job really did become a better opportunity, so my lie eventually looked true. But I still wish I had been brave enough to say, "I'm leaving because I'm miserable."