I think this is great advice. Knowing what you don't know about something is the first step in the journey toward learning more about the topic.
The ability to apply the knowledge you do have, and efficiently learn what it takes to appropriately complete a task is often more valuable than the academic exercise of research without application. I've found that during that time however, there is hesitation which makes people feel less confident, not only in the task at hand, but in their career in general, as some feel their current work and position is the sum of their accomplishments.
I try to resist the feelings of self-doubt by getting energized about learning something new and having a supportive team around me that has witnessed me overcome similar challenges to achieve success. However, some learning and application is done in a bubble, isolated from others' support either by working independently, not having a support system, or failing to sincerely communicate the existential crisis that one feels.
The catch 22 seems that many people that are feeling like an imposture further isolate themselves as they think that communication about their feelings are an insincere attempt at gaining flattery from their support network, potentially perpetuating their feelings of inadequacy. Creative professionals often go through periods of self-doubt, but it's the mature understanding that it's common and occasionally difficult to articulate, that prepares one to overcome those feelings to accomplish the feat.