What blue color job is most comparable to SW Engineering?

While performing my job as a software engineer, I often ask myself, why is this job so hard? You need to keep on studying to be able to do it properly. If it is not language features or paradigms, it is understanding the concepts used in existing code, or trying to understand the math behind some algorithm you need. Or it is digging deeper and deeper in code while chasing a bug. Never it is simply applying the knowledge and skills you already have, even after many years of experience. Then I compare my job to a craftsman like a carpenter or someone who works in construction. How comparable, or not, is it to a software engineering job? Is there a blue color job that gets close in terms of needing to use new knowledge and skills just to be able to execute the job? Don't get me wrong, I like this job, and it is very satisfying at times when one makes steady progress and one can be passionated, even absorbed by it. Do you relate, or is it simply me? I chose blue color in the question because otherwise I would probably get an answer like "any type of engineering".