Does my mind play a part or is it a myth? What do you think?

I'm 27 and been Ttc for 9 months now, without any success. I've had a few blood tests done and so far it's all come back normal. My bmi is normal and I eat healthily, take multi vitamins etc. I am also relaxed and don't have much (if any) stress in my life. This month I have also decided to try preseed (currently approaching fertile stage of my cycle). One thing which I have found irritating is lots of people tell me 'I will happen when you stop trying' or 'just relax, it will happen when you least expect it', 'thinking about it is stopping it happen' etc.. So my question is do you believe it's 'all in the mind' or like me, do you think it's a load of rubbish??  I've always believed that if you want something badly enough, give everything you've got and ask the universe for it, you will get it eventually..! Open to all opinions, hope this will help someone and me also!! :)