This is essentially Wittgenstein’s response to philosophical skepticism (on which The Matrix and similar scenarios— brains in a vat, etc.— are based). He argues that, if you trace back the chain of evidence for any empirical belief, you ultimately come not to a well-founded belief or an ill-founded one, but to an "unfounded way of acting," which is not based in belief but is the basis of it. If we want to function, we must act as if we had reliable evidence for certain things that we really don’t— as he says, "If i want the door to open, the hinges must stay put."

So, he argues that the skeptics essentially misunderstood the situation, because the it’s not that the fundamental aspects of reality seem real to us because our reason has been fooled; we don’t subject these things to reason in the first place. The whole application of "evidence" and "doubt" to these beliefs is, basically, a category mistake. So, stopping at red lights is, in a sense, unfounded, but you’re not actually ever looking for evidence that you should stop anyway.