Silence

Expressing sympathy and especially empathy, for something for which you have no experience, especially when there is no way you would ever have that experience, always comes off as condescension, almost always producing the opposite reaction than you intend.

To put it simply, just don't. Don't talk about something to express sympathy or empathy you don't understand from personal experience, especially when you start with, "I've never...", meaning had the experience, but you think you understand. You don't.

So it is wise to follow the old adage about keeping silent than speaking. It is better to express yourself with friendship than with advice.