Countless factors can cause damage to your roof or contribute to regular wear and tear. Obviously, severe weather is one-factor - hail or high winds can break or tear off shingles. If you have darker shingles, a high UV index can cause those to lose their colour faster than lighter shingles. Another factor can be animals: raccoons or squirrels can set up their nests in attics. In the process of entering, they can cause damage to your roof as well.