Going to try cut a long story short... (haha!)

Saw T today and had some challenging conversations.

We started off with her asking me if I still posted on the internet forum (PC). So I said - Yes. She asked me what I was looking for/hoping to achieve.
So I said I try offer advice and support where I can, and at other times I put up posts asking for help when I'm down and feeling $h*t.
She then asked me how I felt that helped - was I looking for sypmathy or empathy...? Wow - now I actually realised I'm not quite sure I understand the difference between these two words, and I definitely am not sure why it was important to her that I discern between needing sympathy or empathy.
So - that's the first point that confuses me.

Then we carried on discussing the importance of the internet forum (PC) in my life. I said I liked to hear from people who have been through it, who know how things run their course (In my case, the various cycles of bipolar), I like hearing from people that KNOW what to expect...
Then she asked why it was so important that it had to be people that had been through it themselves. Are they the only ones that understand your pain...?
I told her: yes.
So she said: does that then mean that a psychologist does not know what you are going through or what you are feeling, unless they've experienced it too? I kind of agreed with her, but then it became apparent that it was a bit of an absurd statement.

I'm still not sure - can someone know the pain of depression if they've never been there? (Especially if they are a professional, and they should know what you are going through) Do they exercise empathy or sympathy towards you?
How can they understand the various psychiatric disorders without having experienced them?

It almost implies you can understand and learn anything and everything from studying books. Now that makes no sense to me. You cannot expect to be able to drive a car, understand the dynamics of a clutch... by reading a book. Only when you are sitting in the car, does it suddenly make sense.
But our T's read books, and we think they can just understand everything...?

I know I'm mad , but have I really lost the plot?!?