It can happen to churches, to individuals. Remember how long Joash stayed faithful. The challenge is constant, continuing, forever. History is filled with those who started well and ended poorly, history and all the Bible. Add Demas, Diotrophes.
Ultimate potential is impossible without personal convictions.
Joash owed his early successes largely to Jehoiada rather than to personal convictions. One can note the instability of his faith, so that when he prop was removed, he fell. Do not overestimate the importance of personal convictions. Every Christian, every young person, every older person, needs convictions. Not only individuals, but churches.