Think of it as starting a new job. You are hired based on the fact that qualifications match what the employer needs. Your resume looks good. Everyone expects you to do well, but no one knows if you actually will. A few months go by. You do your job well, you show up on time, you are friendly with your subordinates and before you know it they start trusting you. You are the person they expect to show up on time and get your work done quickly and efficiently. You worked hard for your reputation and it starts paying off. A few more months go by. You are late one day and... it's no big deal! Your reputation is strong enough to back you up.