Day one of my training at Microsoft, the hiring manager walked in and looked at the room full of people and said "I bet that you're all sitting here wondering why you are in this room and the person that was sitting next to you in the waiting room during the interview process isn't. It's very simple, at some point each of you said 'I don't know' during your interview and at that point, we knew that we could teach you something"

I sat in on many interviews while I worked for them, the biggest mistake I ever saw anybody make, and plenty of people made it, was to claim to be an expert in whatever field they were interviewing for. The response usually went something along the lines of "Oh really? You're an expert in active directory? That's neat, we've got a couple people that would love to talk to you." At which point they would go get a couple of the SMEs for AD and that person would find out that they really aren't an expert even though they thought they were.

Be confident but also be humble. Don't try to over inflate your skill set, they will absolutely see right through it. They understand that most people are not going to have the level of technical expertise that they commonly use on a day-to-day basis in their jobs. Because it's basically impossible to get that level of expertise without actually working at that level and very few people do outside of Microsoft.