When I first got into shooting in the 70's I was young and read the gun magazines and just about anything else about guns, no internet you know. The 9mm was much maligned as being an ineffective round, probably as much because it was more European and because it wasn't used much by law enforcement so good defensive ammo hadn't been developed for it as much as the .38 and .357 mag. I bought and would shoot Colt .357 mags and Colt 1911's. Glad I did because the value of those guns has made the purchase of them a dandy investment.
Later as law enforcement converted to hi capacity 9mm's to fight the gangs armed with the same in the late 70's and early 80's all of a sudden the 9mm wasn't so denigrated by the gun writers and better ammo and more actual experience proved the 9mm to be better than the .38 spl commonly carried by the police a few years earlier.
I bought a few 9's and enjoyed shooting them, esp. with the cheap ammo coming in from China, and the former Communist countries. The defensive ammo got better and I came to the realization that the 9mm was every bit as good as the .45 for defensive use in anything I would likely come up against and the extra rounds in the mag where more comfort than the bugger slug so while I still shoot the .45's and the .357 and .41 mag revolvers for hunting, fun and at targets I carry my 9's and even a .380 Kel Tec for concealed carry SD and only on a rare occasions drag out a snub nose .38 or 1911 for nostalgia.
Age may not have made me much wiser but it has made me more accepting of adequacy in using something a bit less than maybe the absolute most deadly caliber and round in return for more comfort and concealment.