If you drive on rural highways or roads with heavy traffic, chances are you've experienced having your windshield hit by flying rocks or debris. Windshields are usually strong enough to resist cracking when this happens, but sometimes a large enough stone will cause a crack or chip.
Tiny cracks can slowly grow into long ones over time, so it's a good idea to have windshield chips repaired soon after they happen. Otherwise you may need to replace the entire windshield in the future because cracks over a couple inches are beyond repair.