Good design involves a lot of decision making, and decisions result in trade-offs. Understanding how to go about considering design decisions is critical to good user experiences and ensuring other metrics – such as performance – are not adversely effected to make something "shiny".

On how good designs (and designers) should understand that every decision has impact, and be able to justify that impact:

Now when I point at an interface element, I still expect the designer to be able to justify its inclusion, but I’d also like to know the trade-offs that were made.

On how to think about the impact of a design:

But the downsides tend to be specific to the medium that the design is delivered in.

In print, you can use all the typefaces you want. But if this were for the web, then the calculation would be different. Every extra typeface comes with a performance penalty.

A decision that might be justified in one medium might not work in another medium.

From this perspective, every design decision is like a balance sheet. A good web designer understands the benefits and the costs behind each decision they make.

On the impact of not considering the long term cost of a tech stack:

But often a decision that delivers short-term gain may well end up delivering long-term pain.