Why did the timing belt break at 52,000 miles without warning?

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I brought my mini cooper to East Bay Mini about 2 weeks ago for water pump recall. About 3 days later, every morning I started the car the sound of engine was very loud, but it was back to normal 5 minutes later. I thought because of the cold weather since there weren't any warning lights, and my car just got check last week. The fourth day I was on my way to work the check engine light was on. I thought I could drive to East Bay Mini, but 2 minute later after the red light on the orange light went on, 2 seconds later my car totally stopped. I was lucky didn't have any car behind mine at that time.