What to do?

Ever have that feeling where your gut instinct is telling you something different to your head?
Now I'm pretty much a straight person, and I like to think I'm honest and will try and help anybody as much as I can.. But, sometimes I do think to hold back incase of ruining something rather special. I worry that it'll come out wrong or they'll disagree and then resulting in them hating me.
So what do you do when you really need to say something that is potentially going to go really bad or really good? Make a risk? Or play safe knowing you'll still have your friendship... and wait, incase something goes wrong? then be there to put back together again?
The more I think about it, the more I worry, maybe it's just nerves? Or is it the voice inside me telling me I shouldn't and stay out of it? But, again, when it's one of your best friends life? I don't know, but I want to stay real to the person I am, so I'll probably say it, but there's nothing going to stop me from worrying.
Like they say, a friend who genuinely worries for you, is a true friend. Maybe I'll keep that in mind as I start to open my mouth...