Sending cryptocurrency produces a transaction that appears almost immediately but is not treated as complete for some time. The waiting period exists because settlement on these networks is probabilistic.
Inclusion in a block is not finality
A transaction first sits in a pool of pending items, then is included by a block producer. Inclusion means it has been recorded, not that the record is permanent.
Two producers can build competing blocks at nearly the same time, leaving the network briefly with two versions of history. Only one chain ultimately survives, and transactions in the discarded branch return to the pending pool.
A recipient who treated the first appearance as final could therefore see the payment vanish, which is precisely the failure that confirmation counts are designed to prevent.
Each block deepens the commitment
When a further block is built on top, the earlier block becomes harder to displace, because any competing chain must now replace both blocks and outpace the honest network to do so.
The work or stake required to rewrite history grows with every additional block, so the probability of reversal falls steeply rather than gradually as confirmations accumulate.
Confirmation counts used by exchanges and merchants reflect this curve. They are risk thresholds chosen against the value at stake rather than fixed technical requirements.
Value at risk sets the threshold
A small payment for a coffee can reasonably be accepted with very little confirmation, because the cost of mounting an attack vastly exceeds the amount that could be stolen.
A large transfer justifies waiting longer, since the reward from a successful reversal rises with the sum while the cost of attempting it does not. Custodians handling substantial deposits therefore wait considerably longer than retail payment systems.
This is why the same network can be treated as instant in one context and slow in another without any inconsistency in how it works.
Designs differ in how finality is reached
Networks based on proof of work never reach absolute finality; they only make reversal increasingly impractical, which is why confirmation counts are conventions rather than guarantees.
Networks using stake-based consensus can declare blocks finalised once a sufficient share of validators has attested to them, after which reversal would require those validators to lose their staked assets.
The distinction matters when comparing settlement speeds, because a network that finalises explicitly is offering a different assurance from one that merely accumulates depth.
What users experience as delay
Congestion adds waiting that has nothing to do with confirmations. A transaction offering a low fee may sit unconfirmed for a long period simply because higher-paying transactions are selected first.
Exchanges add their own holds on top, often longer than the network requires, because they are managing customer fraud and account-takeover risk rather than only chain reorganisation risk.
The total wait a user sees is therefore the sum of network conditions, protocol design and institutional policy, and only one of those three is fixed by the technology.