Lesson # 9 disabling button of section Building forms

Hi everyone, So in lesson#9 mosh showed us how we can disable the button and then it’ll work once the validations are all valid but I think its really bad for user because then there’s no way for user to see how can we validate the field?
We should have been told how to show the error message if we are going to keep the button disabled.
What’s your thought on this and if anyone could tell how can we display the error. messages if the button is diabled it would be really helpful.
Thank You