I work as a field tech and this applies to my job as well. New guys will get nervous about the clients watching them, rush, screw things up, miss steps, or just fail to solve the problem.
I drill that mantra into their heads. Slow down. Think about the problem. Think about the systems involved. It doesn't matter if you look like you're just standing there, you're the only guy in 100 miles that can fix it. Rushing means you aren't thinking.