Repeated concussion is dangerous. Years playing in the NFL, suffering multiple concussions each year, maybe you'll lose some of your cognitive abilities.
One or two concussions is okay, obviously you never want to be concussed but if that were to happen, it's fine. There's hundreds of retired league and rules players living perfectly normal lives after suffering lots of concussions in their careers. Plus back in those days, most concussions weren't even diagnosed so just they went back out there!
Best way to stop worrying is to look at the facts. Look at past players, and how they are doing fine. It's just how brain focuses on one aspect of something and we get super anxious about it. Like how some people might think dangerous travelling on a plane is yet plane travel is statistically one of the safest options.