I read What's keeping a malicious man in the middle server from forging a valid certificate?, but when the client goes to verify the certificate, can't an attacker intercept that connection and say that the certificate is a valid certificate? Therefore, an attacker can send a forged certificate that the client could not verify. I don't get what would stop an attacker from creating a MITM (Man in the middle).
What you're talking about is Public Key Infrastructure (PKI). The current implementation of it for SSL/TLS works in a hierarchical trust model. Your browser (and your OS) has a set of Certificate Authority (CA) certificates baked into it, which it trusts. Each certificate contains a CA's public key.
When an SSL certificate is created for a site, their issuing CA signs that cert with their private key. So the public key and details of the site is then signed with the CA's private key.
When you receive the certificate, your browser checks the certificate's signature using the CA's public key, which it has from the pre-installed CA certificates. You can't forge this signature without stealing the CA's private key, breaking the cryptography involved, or finding a bug in the browser's certificate validation code.
The attack you suggested is precisely what tools like Burp Suite can do, but since the generated certificate isn't signed by a trusted CA, the user's browser warns them that the certificate is self-signed.