Your new behavior-based safety process has successfully overcome major obstacles, has good management support, is accepted among the workforce, even has most supervisors on board. The number of observations hits the target and accident rates go down. Your initiative is a success!
A few months later, the number of observations decline. You ask observers if there is a problem and they say, "No, we're just busy and it's hard to get away to do observations." The problem doesn't seem serious, but the number of observations goes even lower and the whole process suffers.