I know this is going to sound stupid but here goes.
When I turned 21 some many years ago I bought my first pistol. It was a .40. I made this decision based on some very very basic personal opinions.
first one was .45 ACP had a little too much recoil for me. I was poor and was not able to put the time in at the range to master it.
The second was ,at the time, 9mm was sooo popular among the gangbangers and mentioned in rap songs that I was irritated about it. I was not going to buy a 9.
So I went with what was between, .40. since then that is all I have ever bought. Also since then I think the majority of police and federal agencies have switched to .40.
I will one day own a .45 but right now I still do not think I will ever be interested in 9mm. Some will say I am missing out and I am ignorant of ballistics on 9mm compared to all other calibers.
I say, no I will not, because there are so many calibers out there and variations of them for me to enjoy that nothing bad is ever going to happen to me just because I decided to be hard headed for ignorant reasons against a 9mm handgun.