I first started cycling seriously in 1990, when I was an intern at Bellcore and had totaled a car that I had bought for $200. The bike was a Shogun, too big for me, but I rode it to work every day, and rode it on weekends. When I graduated and got a real job I got myself a Bianchi Eros and rode that a lot too!
Over the years, I've ridden quite a few bicycles, including tandems, mountain bikes, and various touring bikes. Cycling is, as someone once wrote, a marriage between a body which is somewhat adaptable, and a machine that's somewhat adjustable. But the psychology of the cyclist is actually just as important, if not more so than either the machine or the physical aspects. A bicycle that's fun to ride hard will entice you to ride harder and more often. Frequently people buy bicycles for resale value or for trails or conditions that they'll never ride (or learn to tackle). It's far better to buy a bicycle optimized for smooth roads and only switch to mountain or gravel bikes if you find yourself riding them.
For instance, I learned that while I was a good enough mechanic to fix most parts of the bicycle, and even build wheels, it's not something I enjoy. It's something I'm frequently forced to do so since many professional mechanics aren't even as qualified as I am, despite being more practiced. Many people buy bicycles and do not ride them, and the enthusiasts who pour money into cycling will buy new bikes every 2-5 years, while I tend to retain the same bicycle (and even components) for decades or longer whenever possible. That makes me a very bad fit for the bicycle market. So, for instance, that means that ball bearing hubs which require an overhaul every 2000-5000 miles have a TCO much higher than sealed bearing hubs. Despite owning the tools and requisite skills to do my own overhaul, the pre-load adjustment faff of a ball bearing hub meant that I almost never did my own overhaul, paying a bike shop $30 per overhaul once a year or so.
Similarly, the expensive bottom brackets like Phil Woods just wouldn't get maintained either, and once they needed maintenance, you needed an expensive tool to press the bearings out and install new ones. By comparison, the DuraAce BB cost $40, install without hassle, and when they die (in about the same time as the expensive BBs), are easy to replace. On wheels, sealed bearings almost never die! The only wheel part I ever had die on me were the freehub mechanisms on DuraAce 7700 rear hubs (which are made of titanium and nearly impossible to source!), and the Freehub on the Phil Wood touring rear hub, which cost $300 to replace (and Phil Wood refused to honor their lifetime warranty --- the new owner definitely does not believe in preserving the reputation of the company!).
Cycling is incredibly fashion driven, so over the years I went from being the person showing up at rides with the widest tires (Michelin 25mm, which actually measured 26mm or more) to being the person with the skinniest tire (Continental GP5000 25mm, which measured 25mm). The "gravel bike" revolution isn't bad though --- now you can get high quality tires in 40mm or more, and while I don't always appreciate the roads I used to ride in solitude now having lots of cyclists using them, all cyclists are always better than a car driver.
Many modern "upgrades" such as electronic shifting, disc brakes on road bikes, tubeless tires, and even indexed shifting do nothing to improve the performance or enjoyment of the bicycle, but rather make the bike harder to maintain and subject to unpredictable failures, such as the batteries running out on electronic shifters. I avoid those to the extent possible. Some upgrades, however, can get to the point where a phase change suddenly makes what used to be burden something worth using. One example is that the increase in the number of gears on the rear wheel went from 5 to 9 or 10, all it did was make the rear wheel weaker, as the range of the gears available didn't change all that much. However, when SRAM introduced the 11 speed wide range cassette for mountain bikes with the 11-50 cassette, suddenly you could eliminate the front derailleur while getting a close to identical range of gearing for the bike. At the point it was worth upgrading since a simpler drivetrain wasn't just lighter, it was also more ergonomic and eliminated the unreliable front derailleur. Even for such upgrades I usually would stick to the old tried and true system for a bit longer to give the prices a chance to drop and for potential issues to surface.
There are people who claim that for instance, triple cranksets with front derailleurs are pretty reliable, but they've never been problem free for me. A lot of it is that typical triple setups seem geared towards a 30/40/52 crankset, while I would want the lowest possible gear so I'd go for a 24/39/50 crank. The reality was that this meant that I was running the front derailleur out of spec, so would encounter problems others who didn't ride as low a gear did. In practice, the 50/11 gear almost never got used, so giving up the high gear was the right thing to do when it comes down to switching drivetrains.
I discovered that I enjoy bicycle touring enough to try to do a big tour every year, and love it enough to have written a book on it. The book sells badly, but I have a fondness for it that I don't have for my more successful books. I discovered that I don't like carrying lots of weight on the bicycle even though I've done it a lot. I even bought a triplet so I could carry the kids along, and it was a relief to me that my kids actually enjoy it, never opting to take the train when they have the opportunity to ride. (Though I did learn early on that if they had a sag wagon they would avail themselves of it more often than not!) To be honest they travel better than many adults, never complaining about rain or the difficulties of the day. They finish each day with plenty of energy.
People ask me about ebikes on occasion. I've learned that batteries are the hardest to maintain component on a bicycle. If you use them they wear out and die. If you don't use them, they wear out and die. Sometimes even if you only use them once in a while they break. It's a lot of hassle --- my suspicion is that unless you were an enthusiastic cyclist, an ebike won't make you one and you'll end up driving.
I learned that I really like the geometry of Grant Petersen's bikes. Grant pays more attention to how bicycles ride than most designers. His designs over the years have evolved for the better from an already high standard. I still want to tweak his geometries. For instance, because I ride clipless pedals and he doesn't, I want a BB still lower than what he's willing to use. For a road bike with 25mm tires I want a 80mm BB drop, and he'll go for 75. For a gravel bike with 40mm tires he'll spec an 8cm BB drop, and I think I'd go with 85mm. This sounds minor but when I ride I notice the difference.
I've learned that I'm not sensitive to saddles in general. I went from an Avocet saddles to Brooks B-17s (which never needed breaking in for me) and to Ritchey WCS saddles. The B-17s could last me 10 years before they "broke in" too much to be comfortable, but then I started riding tandems and 2 years of butt sweat would destroy the saddle, so I switched and discovered that the lighter (and more durable) saddles were just as comfortable as the B-17s.
Despite having ridden for 32 years, I'm still learning more about cycling on every ride. Hopefully I'll be cycling for another 32 years!