What is the weird trick that allowed Justin Sun to take over the network? Why was he successful? WTF?
The weird trick...
The weird trick that Justin used is manipulating his connections in the crypto community, paired with buying out Steemit Incs Stake. The trick in that of itself isn't anything particularly novel, its the same thing people do time and time again. Look for an opportunity to seize power, seize power, profit!!! Judging by how poorly he executed his power grab, he isn't very bright. As of right now 2 of the exchanges have already reversed their voting and the original Top 20 witnesses are getting close to retaking control. A smarter manipulator would have got in good with the witnesses first, turned some of them onto his side. A smarter manipulator would have studied EVERYTHING and immersed himself into the culture and become party of the community. A smarter manipulator would have convinced as many people as possible that his vision needs to be supported, so that he could show he has "legitimate support". Theres lots of things Justin Sun could have done differently and he would have fully controlled the chain, but he isn't that smart.
Dumb manipulators burn bridges with people they use, of which he did by putting all these exchanges reputations on the line and forced the exchanges to reverse course within 24 hours. Dumb manipulators don't think long term, they think short term and immediate results, which is why he just used money to buy out Steemit to have SP ready to go immediately and just needed a bit more from exchanges. His exchange manipulation plan was really stupid, obviously the exchanges would reverse course and would bail on him.
Manipulators who use their powers of manipulation to seize power and enrich themselves while not caring about others are a dangerous breed. The opposite is also true, people who are just like 
Short Term what can we do to combat what just happened?
A few thoughts on how you can organize in the short term to make the maximum amount of impact:
*Vote with your SP for the witnesses you think are doing a good job
*Encourage all of your followers and people you follow to VOTE!!!!
*Come up with a few standard tweets people can copy and paste that highlight what Justin Sun is doing(only be truthful and use factual information, no need to name call)
*Identify crypto influencers and decentralization advocates
*Tweet/comment/email those people and use the @ to target influencers on Twitter. Direct message them to!
*Go onto facebook/reddit and other friendly crypto sites and make posts to alert everyone what has happened and how they can help
Long term?
Well, the fact that this happened is pretty alarming. This is a not well known attack vector, but there are some in the crypto community who have talked about this back in 2016 2017 that exchanges could power up or stake cryptocurrency their customers deposit with them.
Why not right? Banks loan out your money that you deposit to them... So you SHOULD expect all exchanges to do this behaviour. The only thing that stopped it THIS TIME for STEEM specifically was that it is a small market coin that the exchanges don't have much to gain. They have MORE to lose than gain in a circumstance with a LOW marketcap value coin.
Bitcoin was taken over and many exchanges went along with it, and the many splits from Bitcoin made the exchanges billions in free air dropped coins. Be wary, the next vector WILL be a fork of Steem that purports to be the REAL STEEM, similar to how BTC currently claims to be the real Bitcoin, but the closest thing to the real Bitcoin is actually Bitcoin Cash(previously was Bitcoin Classic but they stopped development). A chain split of Steem is the likely next move for Justin Sun, or another bad actor.
Community is the biggest thing that can make or break a chain. If Justin Sun forks the chain he needs people to use it, if this community largely ignores him and does not use it then he has no value. The value is in the community and usage. Low community and low usage is death in the crypto space.
Continue using Steem, continue making apps, spreading the word, buying Steem and powering up to vote for witnesses who will secure the chain against bad actors.Do your own due diligence and pay attention! Freedom isn't free, it requires effort ;)