I find that my opinions on money are very different depending on the context. For example - I've got about $60,000 in my stock portfolio, so that fluctuates considerably (anywhere between several hundred and a couple thousand dollars a day). When I see that, I usually just shrug and forget about it. But if I'm out grabbing lunch and one sandwich costs $2 more than another, that really affects my decision.
I get that the investment thing is kind of different because I'm aware there will be ups and downs, and there's the potential (and expectation) that eventually I'll come out ahead (whereas with the more expensive sandwich, there's no way to "make that money back"). But how about this? Say I'm going on a date - depending on the place, I've got a rough idea of how much it's going to cost. Say $100 for the two of us. But if we get an extra glass of wine, or a different main course, or whatever, it could be $120 or even $150. This to me is kind of irrelevant. I wouldn't want to buy the most expensive bottle of wine and end up spending $500, but $100, $120, $130? - it's all the same. Now consider that I had to take a long subway ride to get there, and wanted to bring the magazine I was reading, but I didn't want to hold that or put it on the table during the meal. It cost about $5, and I could have just thrown it away and bought another copy later. That $5 should be inconsequential, right? Especially when I really don't care either way if I spend $100 or $140 on the date.
I guess my point is that I feel like I waste both time and energy worrying about things that have relatively little monetary value. There's that picture frame I got years ago that I'll never use, and I swear one day I'll sell it on eBay and get $3 for it. How can I possibly care about this when my stock portfolio is losing (or gaining) $1000 a day?