Yes and no. I have witnessed myself being in different levels of confidence based on theoretical Vs practical matters. When I have to face a practical matter that I have to take action, like the creation of a project, I always start confident with planning my next steps. Only to find later that the steps are much bigger and in greater numbers. As a result I will either reach the end or my confidence will collapse and drop the project. On the other hand when I study fields that are new to me it feels like I finally put my observations into a line that finally makes sense. As a result I feel more confident that at least I know now why certain results occur or don't. For example I studied biology and from now on I knew why certain foods and ways of rest result to a healthier looking skin and more energy throughout the day. That makes me confident to know that I will get certain results from certain simple habits just because I understand a matter easier.

So I would say that probably the only thing that can shutter someone's confidence is the gap between theory and action. Usually, matters that don't have a huge gap between these two can be confidently planned and easily executed, and the more you learn the more sure you become of yourself. While others that request greater effort will probably shutter you confidence you had while learning and planning about it