There’s a motto in agile software development that says “You aren’t going to need it,” YAGNI. The idea is that when you’re tempted to write some code based on speculation of future use, don’t do it. (I go into this a little deeper here.)
Although “you aren’t going to need it” is a good principle for writing code, the analogous principle “you aren’t going to need to understand it” doesn’t seem to hold. When I try to avoid understanding things in detail, I end up needing to understand the details anyway and wished I’d done so sooner. This has been my experience in math research, software development, and project management.
Obviously you can’t understand everything about everything, and some things you clearly need to know well. In the fuzzy area in between, especially when I’ve said to myself “I hope I don’t have to dig into this,” I’ve often regretted postponing the dig.