[IanCal]

Perhaps you're putting too much emphasis on the "every day" part. The key idea of evaluating whether the shares are worth it now and not just when you bought them is important, to me.

> I don't see how any good can be gained from envisaging a purchase price other than your lock-in price.

If I have a thing valued much higher than I believe it is worth, surely the logical thing for me to do is sell and buy something else that is valued lower than I believe it is worth. The price I paid for it is completely irrelevant (except, importantly, when it comes to taxes but this may not be an issue, much less relevant for many in the UK).

TSLA is ~$256. If I only think it would be worth buying at $100, then why would I keep the ones I own? The purchase price is a sunk cost.