As soon as the bucket gets full they kick it over.
Describes a person's tendency towards self-sabotage. In essence, it describes a behavioural pattern where someone undermines their own progress or success just when things seem to be going exceptionally well for them they self-destruct and will often hurt those around them.
As soon as his business was going really well, a CEO needlessly chose to set up a competing business behind his business partners back discreetly asking all the clients to pay into it. He got caught red-handed and lost everything. This happened many times in his personal and professional life. As soon as the bucket gets full they kick it over.