Do your grammar, punctuation, and usage affect your credibility?

1. Two-question survey

Question Title

1. Does a writer's grammar, punctuation, or usage errors damage that writer's credibility in your eyes? Please explain your answer in a comment, if you like. (Required.)

No, I don't notice errors

No, I don't care

Yes, but I forgive small mistakes, especially in social media posts

Yes, they damage the writer's credibility

Comment? Enter it here.

Question Title

2. What is the worst mistake that writers make? Why is this mistake bad? (Required.)