This is not a problem that can be explained to a 5-year-old except by saying that what you're asking for is so hard that even Google can't do it effectively.

After all these years, we finally found the exception to ELI5 huh? One of my philosophy teachers said something along the likes that what can be explained is limited by the person explaining, not the one being explained to. But I'm no expert on this sp I'll defer to your expertise.