Good advice here Nicole.
When I read it I immediately thought of a recent post (https://medium.com/wdstack/inline-validation-in-forms-designing-the-experience-123fb34088ce) by Mihael Konjević on the very subject of..
“If a user makes a mistake when filling in their details and is met with a robotic ‘invalid error’ message, they feel like they’re the problem.”
You’ll see that Mihael Konjević has done a lot of research specifically on forms and validation. When is the validation happening, when is a field marked as “dirty”, and when are the errors hidden or shown.