I used to believe that what made great designers so great was their craft; their ability to add polish and style to whatever they touched. Now I see that what makes exceptional designers so incredible is not only their attention to detail, but their ability to think holistically about their work.
Long ago, I would spend time browsing Dribbble or Behance and admiring the beautiful aesthetics and animations I saw there. I'd look at portfolios of the most stylish, trendy work for everything from logos and websites to app designs and character illustrations. Whenever I encountered something that seemed highly polished, I'd think: "This is great design!"
It's easy to view design as making things pretty, as though the presentation of the work is all that matters because that's the thing we can see. For those outside the design world, this is a similar perspective to that of art. We tend to celebrate art for its appearance. Apple famously makes beautiful objects and proudly shows them off as such under the veil of "great design."
At some level, this notion that good design is polished craft is true—craft (a delicate process of detail) and visual polish matter significantly in design. But what I've learned over time is that the best designers can think holistic about the work, not just its presentation. They have a keen ability to think and imagine beyond just the design on the screen or canvas.
Inexperienced designers tend to think only within the boundaries of what they're making. They've heard that building a deep understanding of what they're making will strengthen it but often narrow their focus, so they fail to understand how putting their work out into the world might break it apart. The design these inexperienced designers create fails to stand up when it encounters someone with a disability or is taken out of context or distorted by size or time.
Poor design meets one need while creating a dozen others. Good design resolves problems without negatively affecting anything else in its ecosystem.
We call this lens of thinking "systems thinking." It tends to separate the genuinely great designers from the pretty-great ones.
The designers who do tremendous work know that what they're creating does not exist within a bubble. They understand that the context of what they're making plays a vital role in how the team should build it. They know how what they create affects everything it touches, particularly the people. The design is intentional. Trade-offs are known, weighted, and decided on. Not only in the immediate problem space but in the surrounding spaces too.
If you want to be an average designer: focus on a narrow perspective around whatever you're making. Don't worry about how what you make will affect the industry or the people who use or encounter it in different capacities. Don't worry about those who will have to evolve the design or those who might come after you to tweak it.
On the other hand, if you want to be a designer whose impact is beyond a narrow scope: constantly hone your process to consider the range of what—and who—your design work will impact. You can do this in many ways, some of which have been documented in-depth across the Internet.
Build out extremes of your work, the most straightforward and complex versions. Not to say you've done it, but to get a feel for what those extremes look or feel like in context.
Build always with the intent of sharing your work (even if that's not going to happen). Sharing work early and often might mean leaving ample notes or comments in your working documents if you're on a team. If you're working independently, leave the comments anyway. You never know when you'll have to return to some old work and how quickly statements and well-structured documents can help you reconnect and understand the work.
Invite others to provide feedback as often as possible and engage them with questions and curiosities about how their work shapes their perspective of your work.
Look at the larger ecosystem your designs need to exist in, and you'll build things that look better (due to consistency and familiarity) and function better. And that's what makes someone a phenomenal designer.