Why do I stress about saving tiny amounts of money, but fail to recognize that I'm wasting large amounts?

It's like my brain focuses on single small amounts of money but somehow refuses to grasp the concept of large amounts of money accumulating over time, like agonizing over saving $5 while ignoring losing $5000. I'm especially having a hard time with how to view money that I feel I "wasted" little by little in monthly expenditures, but that has added up to a lot - for example, paying $250/mo in docking fees for a boat that I never seem to have time to go on, or paying much more over time for a storage locker than the items inside were ever worth, or paying stupidly high bills for years for a cell phone or cable tv just because I was too afraid or lazy to switch service, etc. When I look back at the last ten years or so, I can add up many tens of thousands of dollars that I basically threw away uselessly just because I failed to plan intelligently or understand my own lifestyle.

Periodically I take stock of my budget and try to prune out waste, and succeed in reducing some of the little things, but can't seem to recognize the big losses except in retrospect. By nature I'm very frugal and always want the best deal, and almost never splurge or even buy anything new for myself unless I truly need it (the boat was my father's by the way). Or I'll waste hours online shopping just to save $10 on something. But a lot of times (like now), I look back at those thousands of lost dollars in terms of things I could otherwise buy and enjoy (opportunity cost), like some amazing vacations, or a top of the line PC or a really nice car, or even just more savings, and I stress out and beat myself up over being so dumb and wasteful (though admittedly, I'd probably also feel bad about splurging on myself like that, and so likely wouldn't do it in the first place).

But other times, I look back and think to myself, oh well whatever, I can earn that money back eventually with working, and what's gone is gone so just forget about it, and why even waste my time striving to save a couple bucks when I lost 100x that already. This temporary mindset makes me more relaxed and less irritated at myself for a while, and less worried about optimizing every cent day to day, but then the next time I think of something that sounds nice to have, I again think, damn, I could have easily bought that and then some if I wasn't such an idiot for so many years. But nonetheless, I still somehow continue with this same kind of wastefulness and messed up perspective.

Each month's expenses individually feel like not that much and so I put off doing anything about it, and I still get by well enough (I have no debt), but then I inevitably kick myself whenever I look back at things.

How can I adjust my mindset to best manage this kind of situation?