When you guys say that someone isn't good enough for medical school, what does this mean exactly?

I'm currently getting my bachelor's in a typical premed degree and I'm really scared I won't make it.

I've been getting As in some classes which are considered difficult (orgo, biochem, physiology, anatomy). I'm not a smart person at all. I did bad in school all throughout my life but I also never studied. Just masturbated and played video games. I had to go to a community college and then transfer to my local University when I finally got the motivation to do something with my life. Once I learned to apply myself I can achieve good grades, but I also feel like the classes really aren't that difficult at all if you follow what the professor says.

I'm basically afraid of spending all this time and then not getting accepted anywhere. When do I know that it's time to give up and find something else?