Generally, Septic systems fail due to lack of maintenance. When the septic tank is not pumped on a regular basis it will become overloaded with solid waste. The overloading will cause the solid waste to enter the cesspool (drainage area). The cesspool will become clogged as it is not designed to handle solid matter. This will cause the system to overfill leading to the possibility of waste backing up into the household.
A properly installed septic system with proper maintenance will provide many years of trouble free service in most cases.