> either you understand the science, or you don't understand it, with no ground in between.

"Understand" in the sense of being able to make accurate predictions about events that have not yet been observed, or more generally in the sense of having a generative model that can give accurate explanations of things you haven't encountered before, even if they are things that have been observed (by others), is black and white: either you can do it or you can't.

If you have limited time to spend on understanding in the above sense, then your ability to do the things described above will be limited. And note that that is not just true of science; it's true of the other areas you mention (law and health) as well. If your knowledge of the law is limited, your ability to predict the legal risks involved with a planned action, or the likely outcome of a legal dispute, will also be limited. Similarly, if your knowledge of medicine is limited, your ability to judge what doctors and other medical professionals tell you--whether it has an actual firm basis or is just them guessing (and the latter is far more prevalent than many people like to think)--will be limited.

> if you know the limits of your understanding. You need to know when the time has come to seek help of a qualified specialist.

You're assuming that there is a qualified specialist in the area in question. And you're also assuming that you can trust the qualified specialist, or at least that you can spot when the qualified specialist, because of some other agenda involved besides helping you, is giving you information that you shoudn't trust.

None of those assumptions are likely to be valid in cases where it matters. First, if "qualified specialist" means someone who does understand the domain in question in the sense I described above--they can make accurate predictions and they have generative models that give them accurate explanations--then there are no qualified specialists in most domains of interest. Certainly that is the case for the law (lawyers would say they are "qualified specialists", but that doesn't mean they can actually do the things I described above--when they predict an outcome, what they're actually doing is telling you they believe they can manipulate the outcome that way, and that depends on how much money you have to spend and how good the opposing lawyers are). It is also the case for many areas of medicine. (Some areas of medicine, such as particular surgical procedures or particular well-understood diseases, do have qualified specialists who can do those things. But that is a small subset of all of medicine.)

Second, even if we take a domain like physics, where in many areas there are qualified specialists, that doesn't mean that you can read pop science books by those qualified specialists and get an understanding of the physics from them, even if you accept that any such understanding will be limited. Many of the things even Nobel Prize winning physicists say in pop science books and articles and videos are not well established physics, they are just that particular physicist's opinons. And if you yourself aren't a qualified specialist, you have no way of knowing when the physicist is telling you well established physics and when they are just giving their opinions. So even in this hardest of hard sciences, "seek help of a qualified specialist" doesn't actually work well as a strategy.