- The Inmate Are Running The Asylum by Alan Cooper
- The Design of Everyday Things by Donald Norman
(and I'm sure there are many more good resources that are recent than that.)
It's very easy as tech-savvy people like us to underestimate how hard technology, even conventions like laundry symbols, are. I personally have printed out a legend explaining the laundry symbols and put them near to my washing machine, but I'm the only person I know who does that. Everyone else guesses or struggles to use laundry symbols correctly, or reads the text in English if it is provided.
Now, does that mean we should change all the laundry symbols just because one person shared a redesign on their blog? No. Changing something that is so well-established has significant downsides and risks. But I think it's perfectly legitimate to spot their difficulties, and to pursue better UX relentlessly, with testing with real users. That's what separates a good (UX) designer from an engineer who produces something that fits their mindset but not the mindset of actual users.