You've highlighted it yourself - value is subjective. Monetary value is just one metric.
exactly
with the op's example of investing money into something which is later sold - you'll maybe find this with cars - if you're restoring a classic car you may well invest some funds into it for which you'd not expect to see a financial profit.
...presumably then the wife gets pregnant, a classic sports car is pushed down on the list of priorities and eventually sold as the cash is now needed for other things - a financial loss may well be made but the return was from the use of and enjoyment of owning the car and getting it running again etc...