If your site is a medical, legal, or financial site, then having a good E-A-T is crucial. Your site may also be considered YMYL if your site gives advice that helps people make an important decision. You are likely also YMYL if you sell products from your website.
We personally think that most websites on the web are considered YMYL. You might argue that your site that sells ballpoint pens is not helping people make major life decisions. However, if you’re taking credit card transactions on your site, then people need to be able to trust you and as such, you are almost definitely YMYL.
The QRG tells us that a YMYL site that is lacking E-A-T is to be considered a low-quality site.