The job of a CEO is to lead the charge. The CEO has the vision and an ability to communicate that vision to the team, to customers, and to investors. By its nature, the job is one of communicating optimism. Many of us are probably too optimistic, but without that optimism, it's difficult to spark the enthusiasm and energy that are critical to a company's success.
At the same time, that optimism can lead to disaster. Sometimes you'll underestimate risks of a new customer contract or costs of a new product development or marketing campaign. You may see a huge opportunity that could lead to the overnight success of the company. But, that temptation to swing for the fences on every pitch usually leads to a strikeout. If you have your head in the clouds, it's hard to keep your feet on the ground. So, how do you do both?
Find someone who understands and respects the forward charging requirements of a CEO, but who can pull your feet to the ground from time to time. Recognize the value of conservatism as a balancing factor in the success of the business. Look for someone who can be your watchdog in terms of legal and ethical issues.
These people are rare, so if you find one, keep her/him close and don't underestimate their value to the business. This doesn't mean you won't take risks or that you'll always follow this person's advice. Your role as CEO is to gather all the information, assess the risks realistically, and then make your decision. With a bit of luck and common sense advice, there will be plenty of opportunities to take a big swing without risking it all.