All statements are of probability, then all principles are heuristics.

All statements are statements of probability, and the vast majority of the time, that probability is not 1 or 0 (that is, 100% or 0%). This is one of the most important things to realize, because it has many consequences.

For instance: consider a situation in which you wish to determine if a decision you made was correct or not. The naive approach would be to analyze whether it had actually positive or negative effects. In certain fields this would be called results-based analysis, and it is generally understood that it is a fallacious approach. The only thing that matters is if the decision, at the time of its being made, had the best expected outcome of all potential decisions. Now, this fact itself must be assigned a probability: that is, the only thing you can determine (or rather, estimate) even after the fact is the probability that the decision was correct. One could do this by re-calculating the expected outcomes of the original potential decisions, and from this calculate the probability that the chosen decision had the highest expected value. At this point we should remark that here, the actual outcome of the situation does affect the calculation. In particular, it should have an effect on the re-calculation of the original expected outcomes.

But up to this point, it is not clear how the pursuit of the "probability that the decision was correct" relates to the ways in which you should alter your decision-making process. After all, knowing if a decision was correct or not has, on average, little merit: unless you are a forecasting genius, most of your decisions will not be correct, and so the after-the-fact knowledge will only induce regret. On the other hand, it is by definition useful to improve your general decision-making.