Understanding Bitcoin's Chain Rules and Reorganizations

I was reading about chain reorganizations and found out that a reorg happens when your node gets blocks from a new longest chain. It basically drops blocks from the old chain for the new one. This helps all nodes sync up and agree on the same blockchain version since the longest chain is the accepted one.

You kinda nailed it there. The best chain is really the longest valid one, but it’s not just about block count, it's also about the difficulty involved. So if two blocks are mined at the same time, the one with higher difficulty takes precedence. If Block A and Block B are valid but A is tougher, B becomes stale. It’s all about which chain has the most work put into it.

To add to that, it's not always about the longest chain, but rather the one with the most accumulated chain work. Otherwise, a longer chain with less work could trick nodes into accepting it. Normally, though, the most work chain is also the longest. You can see chain splits on Mainnet sometimes, and they’re pretty interesting... I tried checking out Testnet4 but it looks like that site doesn’t support it.