Small rocks can cause damage to the windshield when traveling at high speeds.
Rocks are picked up by other car tires and then are thrown backwards. This is just an example that can cause damage to the windshield.
Luckily if the damage is not big and the crack did not spread, there is a way to fix it and save the vehicles windshield.
The faster you fix a small crack; the less the chance that the crack will spread.