In The Courtier, Castiglione made the following puzzling remarks: "For men demonstrate their courage far more often in little things than in great. Very often in the face of appalling danger but where there are numerous witnesses one will find those who, though ready to drop dead with fear, driven on by shame or the presence of others, will press forward, with their eyes closed, and do their duty, only God knows how. But in things of trifling importance, when they believe they can avoid danger without being noticed, they are only to willing to play for safety."
True character, he was saying, exists in the small stuff, in how you behave when no one is watching. It is not about how you perform in the spotlight.
If you only do well in the spotlight that means that you are good at putting on a show, but are not someone others should rely on. If you have one set of manners in public and another in private, which is the real you? And how do you decide?
Expand the definition to include any behavior that is trivial or unimportant. When a man is out on a date, what matters more: how much he is spending or whether he has dirt under his fingernails. At the least, poor grooming will warn off most women.
And if you are having a lunch interview for a job, what matters more: your command of budgeting or the way you talk to the waiter. I hope you have learned that the person who is disrespectful to the waiter or the busboy will be less likely to get the job.
How do you develop good character traits. By practicing them all the time, even, or especially, when it does not matter or when no one is looking. Don't think you are a good person because you can turn it on when you absolutely need to.