I don't know how it can do that. I don't even understand what it means. Does it mean stupid people act stupid? Does it mean you are only stupid if you act stupid?
And, it's fiction so it isn't actually that. It was designed as sappy wisdom to make people feel melancholy and nostalgic. But what it has become is a quote used by many as pseudo country wisdom. So even if that was in reality what it was, it isn't that anymore. It has entered pop culture as supposed simple country wisdom.
And frankly, most of this is tongue-in-cheek in what I thought was the spirit of this thread. I really don't care if people love Forrest Gump, find wisdom in it, or are touched by it. It's not for me, but you do you.