In one interview, I knew some of the people I interviewed with. I was comfortable and confident, but I didn’t get the job. What happened?

It's hard to tell, but you may have been too comfortable. When you walk into an construction interview with people you know, sometimes you relax too much and fail to demonstrate the skills needed to fill the role for which you are being evaluated. Never relax too much. Treat every job construction interview as a formal evaluation of your skills.