When it’s safe to copy something
It’s tempting to copy other designers’ work. But some interface elements are safer to copy than others. Here are some factors. Not all of these are relevant all of the time. Some of these work with or against each other.
Is the element necessary for an interface to function? This is a spectrum. Buttons are more necessary than illustrations, so buttons are safer to copy. UI kits are an extension of this idea. They help you copy the necessary stuff so you can focus on the unnecessary stuff.
Interface approaches like rounded corners on buttons have become standard enough that no-one would suggest you copied another designer.
If something is easy to notice or identify, it’s less safe to copy. People might notice that you used the same bold colour palette as another designer. But no-one notices if you use the same dark blue.
This is similar to noticeability. If a design element is more expressive it’s less safe to copy. For example, it might be safer to copy illustrations made of simple geometric shapes than illustrations made of brush strokes.
If an element uses a common concept it’s safer to copy. There is a spinning globe on the Stripe website. Stripe put a lot of work into it. Lots of websites have since added spinning globes, but I’ve never heard someone claim they copied Stripe. I assume a globe is a universal concept, so Stripe can’t claim it.