To sum this up, I think it is not the rules or principles that people don't understand most of the time, but their own psyche that makes them deviate from the plan. I think we all have an area in life where we can empathize with that.
Last but not least and this is bitterly true, there is also a lot of stupidity in laziness in finance. I didn't want to exclude this in any way.
But I wanted to add to the spectrum that I believe for some people it is really hard because of the way they are wired for whatever reason. The fact in this case often happens to most people and it does not mean that they were wrong from the start but in the middle there are always disturbances especially in terms of emotion and mentality that make them lose control of themselves which makes them not think clearly which results in not a few people who eventually get lost in the middle of the road even though the initial intention and principles they uphold from the start are right.