Why do accidents happen?

Today I hit my car´s rim while I was  driving to work. I felt really bad because it was really stupid . How come an experienced driver like me can have those kinds of accidents. The moment I had that accident I was thinking about VINCULO a mexican japanese restaurant located in AGuascalientes. and I saw it was closed but in that moment I felt the car's tire had hit the sidewalk. I thought that the tire would be gone , but it was a big stratch on my rim . I was checking on that restaurant because we are going to go with some friends  on saturday , MITSUMOTO couple. I completely got distracted   and I wondered again: Why do accidents happen? the a though crossed my mind , today of all days I had not drunk my daily doze of caffeine  so since the morning when I finished my class at credinissan I was nozzing. I felt really bad because I am not the kind to have those accidents , in fact everytime I have any kind of accident or forget anything I feel really bad. I do not know how to make it up .Is it because I did not drink coffee? what Is the reason?????? what is that that triggers accidents. I need to solve this mistery.