although you never have had trouble in a car, you've got to be far more aware on a bike: things like fuel spills / gravel / grain / drain covers / wet leaves that you might not worry about with a car, can (literally) be a case of life or death on a bike. Without any protective shell, you're far, far more vulnerable if anything does go wrong. In a car, a minor bump might result in a bent wing and a minor insurance claim; on a bike, that same bump could well result in broken bones, days (or weeks) in hospital, and months off work with no earnings. The other bit is that car drivers often don't notice bikes anyway - therefore, its up to you to notice them. You don't NEED to do anything stupid to land up in trouble.
The other bit which you sometimes find, is there can be a lot of bulls*** when it comes to bikes, in so far as there are people who'll tell you that you're somehow not "real" if you have anything other than a 1000cc rocketship.
Also, if you're planning to go out on group rides etc, peer pressure is something to be aware of: its all too easy to be encouraged to go faster than you should / are safe with.