Everyone loves to talk about the 21 million cap, but we almost never talk about Bitcoin's dirty little secret: the year 2140.

That's when the block rewards officially run out. No more new Bitcoin. From that point on, the entire security of the network—the miners who protect it from attack—will rely only on transaction fees.

The theory is that a mature, global Bitcoin network will have enough fee volume to pay for its own security. But is that a guarantee? What happens if Layer 2 solutions thrive and most transactions happen off-chain, starving the main chain of fees?

Are we placing our faith in a future fee market that might not be strong enough to secure a multi-trillion dollar asset? Or is this a non-issue that the protocol will naturally solve?

Is Bitcoin's security budget a fatal flaw we're just kicking down the road?