IMO, the most surprising part about BTC for me and probably for most people, is how incredibly resilient it is. BTC started out of dissatisfaction with the fiat system and in the beginning was almost worthless, but Bitcoin managed to get through a series of major crises, followed by the collapse of several exchanges like Mt. Gox and FTX and even bans in various countries yet BTC still survives and grows.
Many speculated that BTC would die, but instead it grew into a major asset with huge capitalization. Of course, for me and especially for those who were around at Bitcoin's early days, the hardest thing to believe now isnt just that its price once topped $126k, but the widespread adoption. Even the US became the largest holder of BTC, El Salvador made it legal tender and a few companies use BTC. So, the original BTC concept was considered unlikely to last because no one controlled it, but now it's a national strategic reserve and a valuable asset which would have been almost impossible to believe in Bitcoin's early years.
The adoption of Bitcoin as a national strategic reserve was something no one thought would become a reality in the early days. This is surprising to many. Especially old Bitcoiners like myself. For Bitcoin to reach this far, it means it's already a "force to reckon" with. Just like Gold. It will be with us for generations.
17 years in the making, yet Bitcoin has emerged bigger and stronger than ever. Imagine what surprises we'll find by the next decade. What's important is that Bitcoin stays true to its roots of decentralization and censorship-resistance. The day it gets compromised, will be the end Bitcoin will die for good. I'd pay close attention to the network, just in case.