Well, it is possible also to fear something known. Like pain. I have hurt myself bad while skiing, so now I get scared when I get into similar situations while skiing that I consider at high risk of causing the pain that I already experienced. But it is probably easier to control it, not let it overpower you into irrational decisions when you fear the known vs. fearing the unknown. Although some people do get irrational even about fearing to break a limb for a second time.