Bitcoin transactions, hitchiking, statistics and cointape ...

A friend wrote ... "look at this transaction (link to blockchain.info) ... it seems fine, yet 3 hours later it's still not through? it's even high priority".

Blockchain does have a pretty outdated way to flag transactions as "high priority". Said transaction had a 0.0001 BTC fee, was 520 bytes big, and according to https://bitcoinfees.21.co/ (aka "cointape") it had a 90% probability to be between 3 and 20 blocks delayed. However, I think it's a common misconception that when those 20 blocks have passed, the transaction should go through - that's not entirely how it works.

If we assume every miner is using the default settings with bitcoin core, the mempool queue is sorted only by fee paid divided by transaction size. This means that the probability is not dependent on time passed. Transaction still not confirmed an hour later ... bad luck, everything else being the same, there will still be between 15 and 200 minutes waiting time.

I used to hitch hike a lot when I was younger, I believe it compares quite a bit. At any point of time, there would be an average of 20 cars passing without stopping for me. One more car passed without stopping - bad luck, one can still by average expect 20 more cars to pass by. I'd gone mental if I wouldn't be able to fill my head with more cheerful thoughts than statistics and geometric probability distributions. Bitcoin is even worse - having paid too low transaction fee, it's like being at the very tail of a long queue, but instead of moving forward in the queue one is actually moving backwards, as the other transactions with higher fees paid are constantly cutting in and entering the queue somewhere in front of you rather than behind.

There are many factors contributing to successfully getting a hitch from A to B. My wife was even participating in hitchhiking competitions back in those days. With the bitcoin transactions, it's mostly only the fee that counts. Perhaps hitch hiking isn't the best analogy, hitch hikers usually don't pay for the ride (then they aren't really true hitch hikers). Anyway, it's maybe not entirely unreasonable to compare the low-fee transaction with a visibly drunk bum trying to hitch with a beer bottle in his hand, while the high-fee transaction is an attractive-looking young woman, situated at a place where the traffic passes slowly and where it's easy to stop.

In the former days, the blocks was like a mix of small buses and smaller cars, but the very most of them had friendly drivers and lots of free seats, they would almost always stop for hitch hikers. If the probability is above 50% that one will get a ride with any car passing by ... then it's not that depressing to watch yet another car pass by. Nowadays the very most of the traffic are small buses, the road is full of hitch hikers and the buses are full of premium-paying customers, so they for sure won't stop for hitch hikers.

Pragmatically, if one wants to get a bitcoin transaction confirmed within a reasonable and predictable time, one really should pay "premium fee" for it ... but there are only so many seats on those buses, paying the "premium fee" causes other transactions to not be included. I believe that if Bitcoin is to thrive (and not just being a fringe thing where some few rich hard-core bitcoiners are using the protocol to push containers with digital gold across the national borders and/or away from taxation) we really need to set in either bigger buses or more of them ...