Well, to start with, what you are describing is not subtlety. Subtlety is paying attention to the small but significant details of something -- making a subtle point or a subtle distinction.
What you are talking about is indirection: suggesting one thing by saying another. It is closely related to the old saw "show don't tell". What show don't tell means is that instead of telling us, for example, "Tom was nervous", you tell us something about Tom which may lead us to conclude Tom was nervous such as "Tom chewed his fingernails and shuffled his feet." This is still telling, of course. But you are telling us one thing in order to get us to conclude another thing.
The advantage of this indirection is that people are more apt to accept conclusions they arrive at themselves than propositions you make outright.
This can be particularly true where there is an element of opinion or judgement involved. If you can get someone to a make a judgement by telling them concrete non-controversial things, they are more likely to accept what you say and then to arrive at the same conclusion for themselves.
But there is a downside to this. While the reader may be more accepting of the conclusion if they arrive at it themselves, you can't guarantee that that they will actually reach the same conclusion as you. You may believe that if told A and B, the reader must necessarily conclude C, but some portion of your audience is going to conclude D, and one or two wingnuts are going to go on social media and castigate you for saying E.
The trade off for the power of leading the reader to draw their own conclusions is that some will draw a different conclusion. There is nothing you can do about that. It's the risk you take when you practice indirection.
Some authors will hedge their bets by tacking on the desired conclusion: "Tom chewed his fingernails and shuffled his feet nervously." But here you have given up much of the power of indirection. By taking the reader directly to the desired conclusion you have prevented them from discovering it for themselves and therefore weakened their attachment to it.
Not, of course, that there is anything wrong with stating a conclusion and the evidence to support it. This helps bolster your argument when you argue directly. But if you want to write with indirection and lead the reader to an unstated conclusion, you give up the certainty of their reaching the conclusion you intend.
Incidentally, this is perhaps the reason the adverbs get such a bad rap in fiction writing. The are often used to force the implication of "showing" into the open, a kind of showing with a chaser of telling. And yes, that is precisely a case of not trusting the audience and/or of not trusting yourself to tell the things that will lead the reader where you want them to go.
Learning to lead people more reliably is not really a matter of writing technique but of understanding how people think and form conclusions. If I tell people A and B, will the majority conclude C? While this question is at the heart of rhetoric, nothing in writing technique is going to tell you. That comes from experience and possibly from the study of other disciplines.
The one thing we could perhaps suggest as a writing technique is that indirection works by a kind of ven diagram. If A and B don't get everyone to C, maybe you can fix some of that by adding another statement D. The overlap of A, B, and D is smaller than the overlap of A and B leaving less room for the reader to reach different conclusions. But this technique has its limits. The reader can only hold so many ideas in their head at once and, because they are seeking a conclusion, they are likely to make up their minds after A and B, or possibly after D, and either dismiss or falsely integrate statements E F and G into the conclusion they have already reached. Choosing the best possible A and B, therefore, is usually better than parading out A B D E F and G (though again, this can have its place.)