Quite a bump, but I feel it's necessary - I've become the very example I gave in my OP. Earlier in the year I bought some tickets for Jacob Banks in London (he's decent, check him out). And now, just a night before the gig, me and the wife can't be arsed with traipsing up to London on a week night, spending money on travel, food and drink, to get crushed in a crowded standing-only venue. Too tired, too skint, not passionate enough about the artist. My wife argued that we're wasting the money spent on the tickets, but I expertly (I'm an expert) argued that it would be wasting
more money if we went to the concert that we no longer really want to go to. The money spent on the tickets has long gone, spending more to stop the initial money being "wasted" is a fool's errand.
The sunk cost fallacy has been defeated, all hail cold logic!