What makes a GFCI go bad?

In the realm of electrical safety, GFCI (Ground Fault Circuit Interrupter) devices play a crucial role in preventing electrical shocks. However, these devices are not invincible and can malfunction over time. Could you elaborate on some of the common factors that contribute to the deterioration of a GFCI? Are there any specific signs or symptoms that homeowners should be aware of to identify a failing GFCI? Additionally, how frequently should GFCI outlets be tested and replaced to ensure optimal safety? Understanding these points would greatly assist in maintaining a SAFE electrical environment in homes and offices.