So why can't people accept mental illness for what it is?

It's World Mental Health Day today. So I thought I'll post something.

I remember stumbling upon an article about Why don’t people accept that mental illness is just as real and devastating as physical illness? and it got me thinking, why?  I once tried to open up to a friend of mine whom I thought would understand and accept me for what I am. I spilled all the dirty things that I’ve kept hidden for so long and admitted to the succumbing to my darkest thoughts at my frailest moments and it was a big mistake. She didn’t understand. Apparently, I was too caught up in my own dark world that I’ve became “who I thought I was”. I needed to start thinking positively and chuck the meds as soon as I felt better. Needless to say, I clammed up straight away and disappeared from the radar.

So why is it so hard for people to understand that we can’t exactly control our actions or how we’re feeling?