When you meet problems or a target then you say to your self, "I Can't achieve it" or "I Can't do it", it means you close the door & you close your opportunity.
So, what should you talk to your self? I think better u say to your self "How can I achieve it?" or "How can I do it"?, it means you open your door, open your heart, open your mind, and open your opportunity for improvement.
So, if every things goes realistic, never say " I Can't ", but always talk to your self first. "How Can I"?
Life is about problems & target. How can I solve the problems? How Can I achieve my targets? then..Action!
The point is "how self talk working in your self". Positive..Positive.