The reality is we all "think" we know what is good or bad.

But do we really? A lot of it is misguided information. When we start testing before and after meals we begin to see the real and very immediate impact of what some "good" food may have on our glucose level. Sometimes it may just impact us, no problem for others. And this little bit of information goes a long way to improving our condition. It helps us to understand whether simple/complex carbs has any impact and eat accordingly. Fats eg avocado, nuts, pork belly, knuckles, some dark chocolates have little impact for me.
Low fat food often have added sugar. Low sugar food doesn't mean low carb. And the total amount consume makes a difference.
When I tested high after a meal, I usually drink tea to bring it down. It works for me.