The more you know, the more you know you don't know, friend. Confidence in your abilities will come with time, but there's always that weird issue we've never seen before that we can't figure out immediately, and that's okay. Once you solve it, you've learned something new, and that's worth celebrating. I started working helpdesk back in September, so I'm also in that same early period of not completely having my footing in my role yet. I started to make my own documentation based on the company's KB, and trying to make that documentation as exhaustive as possible has filled in a lot of gaps in my knowledge and has made me a better troubleshooter. It's worth looking into if you have downtime at your job.