I know nothing about the subject except that my garage and backyard are littered with the "good deals" I should have passed up. I still have trouble passing up those "deals" that are of negative value.

Negative value is an idea that we should all learn.
Say I find a 1954 New Yorker that I can buy for $200.00. It's a great deal, right? Wrong. That car has negative value.
In buying it I have signed myself up for at least several thousand dollars of expenses before I can even use it. If for some reason I do not use my $200 New Yorker, it will sit there and depreciate forever. My $200 will sit there with it, and I can't even buy beer with the money.

Now I may decide I am willing to invest those dollars and hours because I really have always wanted to drive and own a 1954 New Yorker. If that's the case it IS a great deal, but that $200 purchase still has negative value. Ecomnomists call it "Opportunity Cost". Why? Because by putting that $200 into something, I have passed up the opportunity to invest in something else, which could be better.

If you find yourself using the word "just" in describing the object, it most likely has negative value. "It just has to pass cert." "It just has to be modified to fit my car." etc.

As I said to start, I have learned this lesson many, many times and am weighed down by all the negative value I have piled up over the years.

R.