Point of view: May I ask a personal question?
When someone says that, what are they asking? They're asking for permission to enquire about something you may not be comfortable talking about because it's private. It's not something you would normally share publicly, hence the need for permission. (Especially if you are British.)
What makes something personal? Uniquely yours, concerning your private life (is that still a thing?), your emotions, desires, hopes, dreams, relationships, secrets. This is an interesting inversion, since the root of the word – persona – literally means 'mask': the kind worn in...