I think the answer is, beforehand there are too many contingencies and it seems like a waste in mental effort to consider them all.
Consider the stock example, which is quite simple. I buy a share at $100. I don’t think it’s so simple that I decide in advance I’m going to sell if it drops below $80. What if, in one day, it drops to $83, and I don’t have access to a broker except to sell it at the end of the next day? What if the stock is doing well, and then there’s a rumor that quickly sends it down to $80? What if I happen to have good reason to think the rumor is false? What if it’s doing very well, but then a rumor sends it down to $85? And this time, I think the rumor is correct. What if I’m away from my broker while bad news develops and it drops to $50, but then the bad news appears increasingly not so bad and the stock is rising when I get in contact with my broker again? Etc.
And all this has to do with when to sell a share of stock, which is seemingly characterized by a single number. There is much more that can develop in connection to the scenario you describe.
I think the answer is, beforehand there are too many contingencies and it seems like a waste in mental effort to consider them all.
Consider the stock example, which is quite simple. I buy a share at $100. I don’t think it’s so simple that I decide in advance I’m going to sell if it drops below $80. What if, in one day, it drops to $83, and I don’t have access to a broker except to sell it at the end of the next day? What if the stock is doing well, and then there’s a rumor that quickly sends it down to $80? What if I happen to have good reason to think the rumor is false? What if it’s doing very well, but then a rumor sends it down to $85? And this time, I think the rumor is correct. What if I’m away from my broker while bad news develops and it drops to $50, but then the bad news appears increasingly not so bad and the stock is rising when I get in contact with my broker again? Etc.
And all this has to do with when to sell a share of stock, which is seemingly characterized by a single number. There is much more that can develop in connection to the scenario you describe.