Bitcoin aims to give people self sovereignty and financial freedom (who otherwise couldn't attain it). That's a noble goal, but the project has always had a fundamental problem:
Bitcoin only survives if enough miners continue to participate, who spend on electricity to keep the network's total hash rate high (enough to fend off a determined foe, including one focusing state-level resources in a short period of time to pull off a 51% attack). Miners do this in exchange for new bitcoin. Though miners' profitability has recently been challenged by the latest downturn, the market can adjust and is not in immediate jeopardy of collapse. But it will be.
The total supply of bitcoin is 21M. Less than 2M remain to be mined in the project's lifetime.
Eventually the # of bitcoins produced per year will be too low to maintain miner incentives. [Every four years moving forward, half as many bitcoins will be produced. The so-called "halvening" has generally been seen by investors as a positive thing, b/c it implies continued scarcity, but they miss the forest for the trees.]
Today, the amount of electricity used to safeguard the bitcoin network is roughly equivalent to what a small country like Argentina consumes. Historically, new bitcoins are created to reward miners who pay for that electricity, but that is increasingly less the case.
Transaction fees would need to increase to pick up the slack (of lower mining profits). Ever-higher transaction fees will kill the cryptocurrency's potential for mass appeal (which companies like Square(Block) have bet big on).
The only way that none of this is an issue is if bitcoin continues increasing in value inexorably. To be fair, I'd say that's Bitcoin's #1 use case so far has been: a speculative vehicle that consistently rises in value. That will inevitably come to an end, if for no other reason than there isn't enough money in the world to sustain its historic rate of climb. It's also dubious for something to be branded as digital gold if it requires more new money coming into the system to be viable, in that respect it's closer to a Ponzi scheme.
Another "out" is if all of the miners can agree to increase the project's total supply, something I imagine will be attempted. That will be a huge shit show though, as the brand of bitcoin revolves entirely around scarcity.
That's the project's basic flaw. I set aside bitcoin's less-existential problems: extreme energy demands, failure to act as an inflationary hedge, disproportionate use by ransomware gangs, potential vulnerability to quantum crypto-breaking computing, and existence in a space rife with scams (from USDT to UST and all the under-regulated web3 banks and securities-sellers in between, like Celsius).
[Old edit, now it can be seen on page 2. It likely tripped HN's "flame-war" alarm, which is really a thing: [Interesting, this hit the front page of HN and was shadowbanned(?). I'm not seeing it as flagged, but now it's nowhere in the top 90 posts. Can someone ping a mod, or @dang?]]
To address the Lightning network (which settles transactions off-chain quickly for less $) > "Transaction fees will have to grow in the coming decades, but if most users stay on the Lightning Network they won't be directly exposed to those fees." If users are shielded from the future transaction fees b/c of Lightning. Ok, well where does the money to safeguard the network come from if mining blocks produces less and less of it (and users don't pay fees b/c of Lightning)?