I think it's important to learn that subtleness and significance are two separate characteristics of things and that they don't need to be related. Even though we might tend to act like they are related.
For instance, we might tend to think that subtle/non-obvious things are insignificant/unimportant. Or to flip this around, that significant/important things are obvious/not-subtle.
There's a matrix, then, of possibilities for every thing:
|Subtle||Subtle, Significant||Subtle, Insignificant|
|Obvious||Obvious, Significant||Obvious, Insignificant|
Don't be hasty
It's important to make sure that if you have softened to the notion that subtlety and significance aren't necessarily related, for instance moving away from the belief that subtle things are never significant, that you do not wholly flip over to believing the opposite thing, such as that you now believe that subtle things are always significant.
Subtle things may or may not be significant. Obvious things, too, may or may not be significant.
For people that did once believe in a strict rule, such as that subtle things are always insignificant, could see this maybe-it-is-and-maybe-it-isn't uncertainty as putting a great deal of responsibility on them to decide whether each given thing is subtle and/or significant. And it is a responsibility, but it is one that we should be mindful of so that we don't fall victim to the counterexamples of the strict rules.
(Note that the "strict rules" thing veers close to the notion of mental shortcuts, which are similar to but I suspect subtly and significantly different from heuristics.)