Comment by Svip

In your example, the onus is on the consumer not the provider. I could still be writing code that checks if `err.String() == "no more tea available."`. I agree, I shouldn't do that, but nothing is preventing me from doing that. Additionally, errors.Is is a relatively recent addition to Go, so by the time people would check for errors like this, it was just easier to check the literal string. But as an API provider in Go, you cannot prevent your consumers from checking the return values of .String().