Interesting watching X Factor and hearing so many of the finalists saying of their experiences 'I can't believe it!', without realizing the damage of that mantra...
'I can't believe it!' has the energy of 'things like this don't happen to me' ' I don't deserve this' and 'I've only got this through luck'. So energetically the person unknowingly pushes the experience away.
Far better to say 'I love this, I'm enjoying every moment, I've dreamed all my life of getting here and I want this to go on forever'.
Similar thing applies to the 'I can't afford it ' mantra, it implies lack and scarcity and blocks the flow of more money in. Whereas 'I want this so much I'm going to find a way to get it' opens up the flow to the ideas and opportunities to allow the money to manifest.
Listen to your mantras, they represent the mindset which perpetuates your reality.