Nothing is too big to fail in crypto world, Terra Luna is a big example that the safety of your money isn't guaranteed even if you invest in top altcoins out there, it's the same risk involve with crypto generally including BTC but BTC is just way safer, I have seen people losing 6 figures to Luna and some Defi projects, first of all try to understand what you are going into, many don't know how risky crypto space is, take risks with what you are ready to throw away.
I just created a thread
Bitcoin 101: Share an Unpopular Opinion you hold about Bitcoin with Newbies. One of the comments by NeuroticFish echoed your thought
In the same way Bitcoin can eventually reach $1M, it can also eventually fall to 0.
The truth is nothing is promised. Most of us believe in bitcoin's potential yet we know that there is still some uncertainty. Personally, I feel that there is still a 5% chance that something bigger than Bitcoin may pop up in the distant future.