When you have a positive attitude, positive results will come.
Pessimism, on the other hand, is the enemy of success.
Pessimism is able to turn manageable challenges into ones that are insurmountable, while optimism is able to make every challenge one that you are able to overcome.
Start trying to catch yourself when you are thinking negative thoughts or displaying a pessimistic attitude toward some aspect of your career and replace them instead with a positive and optimistic outlook.
In other words, always look on the bright side and have a positive attitude and the future of your career will be brighter as well.