Improve overlay error messages

[aaronshurley]

Why?

When an overlay matcher’s expectation fails, the error message ytt gives falls short of helping most users determine what to do next.

For more details see the "Problem" and "Analysis" sections in Overlay message errors

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What?

Do this loop until we find a good error message:

1. design a little user research to test an idea of a better message format
2. conduct that research
3. synthesize into one or more user stories (attach to this epic)
4. make those improvements (play the storie(s))
5. design a little more user research to validate the improvement
6. conduct that research
7. if not "good enough", goto 1

Note: By "little" we intend to put in the smallest possible effort that could still yield enough signal that we'll mitigate the risk we build the wrong thing. In other words, it's better to do this loop more times than it would to invest a lot in a single loop.

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Resources

• originating issue: https://github.com/k14s/ytt/issues/94
• public issue: https://github.com/k14s/ytt/issues/95
• Overlay message errors proposals for actual improvements
• Overlay Error Message User Research details of how we're conducting user research
• Thoughts on error message UX:
  • https://uxdworld.com/2018/05/30/how-to-write-good-error-messages
• The Mom Test by Rob Fitzpatrick (See team drive for this book)

[pivotaljohn]

FWIW, the need for this was insightfully highlighted in this conversation: https://github.com/vmware-tanzu/carvel-ytt/discussions/313#discussioncomment-632458