Of course it is important to keep trying to realise your dreams, and optimism about your potential is a great help to attain goals.
Unbridled optimism, however, can also be dangerous if it leads to a stubborn march down a dead end.
The trick is to be flexible in your optimism.
This means that you will have:
1. The strength to change what can be changed,
2. The courage to accept what cannot be changed,
3. The wisdom to distinguish between 1. and 2.
AND
4. Never lose sight of the essence of your dream. What cannot be done now, may be possible at another moment in a different form.