system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why is the Independent Commission Against Corruption in Hong Kong so successful?
gpt
There are a multitude of reasons, so I'll try to ELI5 a few. 

1) Hong Kong is small

Hong Kong is a self-governing city (and will remain so, fingers crossed, for the foreseeable future), so the government doesn't have to deal with different counties, states, or long distances. This makes effective communication and investigation much easier, since you're never going to have to travel far to look into something. 

Being a very dense city, each jurisdiction has a large population. This means that there are a fewer number of jurisdictions overall compared to if the city was more spread out, which necessarily means the total number of civil servants is lower than you would expect for a region with a population of seven million. Fewer civil servants means it's much easier to weed out corruption. 

LI5: if you all live in the same house, and there's not very many of you, it's a lot easier to find out who's been stealing from the cookie jar than if there were a lot of you and you all lived in houses far away. 

2) The ICAC has a reputation

While Hong Kong was under colonial rule, the ICAC was answerable only to the governor. When it was founded in 1974, it replaced a police branch that had notably failed to curb corruption in the past, and so it had an incentive to be rather . . . harsh. 

For example, a mass purge took place in early 1978, where it was announced that 119 officers, including several high-profile or high-ranking ones, were asked to leave under the provisions of Colonial Regulation 55. Colonial Regulation 55 essentially says that the governor can do what he wants; i.e. no trials necessary. Purging all these officers at once made a huge splash in the public consciousness, more so than a trickle-in of convictions would have. Even though the ICAC doesn't have this capability anymore, it still stands as a testament to its investigatory power. 

The ICAC is also purported to have somewhat intense interrogation procedure. Take that as you will. 

LI5: If you find out your friends are stealing from the cookie jar, they might threaten to not be your friend anymore or bribe you with some of the cookies if you don't tell. That's why the ICAC isn't friends with anybody, so it can be mean to people who steal from the cookie jar. This makes it difficult for people who steal from the cookie jar to get away with things. 

3) Much corruption in Hong Kong is/was market-based

Off-course betting on horse races was a huge source of bribery and corruption, because gambling was and remains a large market that the general population (and therefore, police officers) participate in. Hong Kong made off-course betting legal, eradicating the problem. 

LI5: Turns out, many people were stealing from the cookie jar because they wanted oatmeal raisin cookies. Now oatmeal raisin cookies are just on the counter so nobody has to steal from the cookie jar anymore to get them. 

4) The ICAC focuses on education and prevention

The ICAC doesn't just investigate after corruption has occurred. It takes an active stance towards reducing corruption in the first place through education and prevention. 

The ICAC makes clear that bribes and kickbacks are not to be an expected or normal part of everyday life, and reassures citizens that they're on their side and should they find themselves on the receiving end of any corrupt threat that they can turn to it to investigate. 

The ICAC furthermore offers advice and practical help to enable companies and organisations to introduce systems and procedures that are resistant to corruption, making it more difficult for it to occur in the first place. 

LI5: the ICAC doesn't just look to see who is stealing from the cookie jar, it also puts locks on it and teaches people what a cookie jar cookie looks like so that if they're offered one they can report who did it. 

Hope this helps!