It's hard to watch someone you love make a mistake. It's even harder not to say something. So what do you do? You could go ahead and open your mouth, but what's the point? I mean sure, it might make you feel better, but they won't hear you. If someone is set on doing something, what you say doesn't matter. And rightfully so I suppose. You can't learn a lesson on your own if you don't make a mistake on your own.
I would know. Trust me.
So, as hard as it might be, you just have to watch. Show support. Stock up on some tissues. And in the end, hold off on the 'I told you so'.
After all : You can't learn a lesson from a mistake that you haven't made.