Just be ultra honest about the point you want to make with supporting evidence/arguments without being disrespectful. The way you speak to your manager doesn't necessarily have to the same you speak to your CEO, because their motivations may differ (usually do). Speaking to CEO, you should try to be aligned with the company goals, whatever you're speaking about try to connect with company's goals. At the end of the day, that is all CEO cares about. However, manager might have ulterior motives, politics etc. So here you formulate your points without causing too much trouble or insecurity to their position.