Well, it may be a semantics point, but there are no absolutes in trading. You don't "know" what's going to happen 5 minutes from now, much less 5 hours or 5 days or 5 weeks or 5 months. The only traders that "know" are the ones I saw on the PBS Frontline special about Stephen Cohen, et al. And that's no trading system that you or I are ever going to develop ( i.e., inside information on a massive scale ).
The OP makes a cliché but valid observation about having the guts to follow your trading system win or lose.