In my view it's mostly and most importantly happens in the brain, in the thought process. The longer I'm in this game the more I understand its a thought process. And control of the physiological aspects of it is paramount.Sticking to a logical plan, and not getting carried away by other factors.
The human brain is wired to react to 'flight or fight' or in the investing sphere 'greed and fear' they are incredibly powerful forces even within the most discipline mind. I don;t think it is possible to completely overcome our own nature. But it is possible to rein in the most extreme examples of them. Understanding them and accepting them is key to being successful Never assume a decision is right or wrong, A good decision at the time can later be the opposite, Applying a critical thought should constantly be applied to all decisions. And this a great reason to limit the number of investments.