"Develop a healthy disrespect for the impossible." — Gene Hoffman, Supervalu
Impossible is a state of mind; what is impossible today may not be so tomorrow. What is impossible for us may not be so for others. It is not impossible simply because a human mind cannot come up with anything that does not already exist. This means that nothing is impossible if we put our mind to it. To think otherwise will prevent us from finding a solution.
It's easier to say something is impossible, or at least extremely unlikely. Everyone has periods of doubts. Everyone considers giving up sometimes, but then you just have to remember why you tried so hard in the first place.
Never give up. Attitude is a little thing that makes a big difference. The right attitude makes the impossible possible. Attitudes drive behavior. If you want to succeed at anything you need to have the right mindset.