Sek, who only attended four years of primary school before dropping out due to financial reasons, was said to have been an ill-behaved child. His elder sister Sek Yoke Mui said that he was obsessed with Wuxia novels and Kungfu movies in his childhood and had molested his younger sister Nyuk Ngok at age 12. Sek was also said to enjoy injuring himself at times, describing it as thrilling. He and his elder brother Kim Siong fought with other students in school, and both had bad, impulsive tempers. There was one occasion when both brothers were chained at home for stealing a bicycle and fighting. Eventually, Kim Siong was jailed in a boys' home for theft, and was jailed a second time for going AWOL during his National Service. It was at this point, Kim Siong claimed, he started to reconsider his life choices and decided to turn over a new leaf and be more mature; as a result, he restarted his education and later found a stable job as an electrician a few years later.
