Bikes are relatively simple machines... I would venture to say that the ratio of rider vs. mechanical error is grossly skewed towards rider error.
Probably 1000 to 1, if not more.
Part of riding is being prepared for the unexpected.... things happen, do your best to be "heads-up"... we all crash from time to time... and sometimes, very bad things happen.
Lessen the likelihood of this happening by staying up on your maintenance, wearing gear, and riding hyper-defensively.
Be Safe.
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