Riding in a car is just dangerous (compared to most other normal, every day activities). So safEST would be to never go anywhere. But that's obviously not realistic. So, as with most other things in life, you have to find the right balance. Then once you have made your careful, thoughtful decision (about what seat to get, or whatever), you just have to stop thinking about it and rest in the fact that you made a good decision. Obviously if something happens that prompts you to re-think your decision (seat gets recalled or whatever), then you re-think. But you can't be constantly re-thinking everything or you'll drive yourself crazy.
Case in point - my dd is currently riding in a FF Britax Boulevard. It is installed correctly, top tethered, and she fits it just fine. But every so often, someone brings up the transport Canada tests with the forward facing marathons. A long thread ensues where people weigh in on how they perceive the safety of forward facing Britax (classic) convertibles. And you know what, I could drive myself crazy if I re-hashed the decision each time one of these threads came up. But instead, I thought through the decision very carefully the first time I heard of the issue, and now when it comes up again, I remind myself that I have made a good decision and I don't need to go through that process again.