I wrote down my understanding of bitcoin and influence of the block size as a train analogy. Here it is for you to make fun of:

Imagine there’s a train line.
Trains go at regular intervals and have fixed number of seats.

Operator of the train line gradually issues unfalsifiable coins which there will eventually be specific number of and not one more. You can carry any amount of coins while you ride the train. People started to find them valuable so you can buy them before departure and sell on arrival.

Tickets for the train are auctioned for coins. Only the people who bid most can ride the next train. You can even bid 0 coins and get on the next train for free if not enough people outbid you.

Making train go is the cheap and easy part. What’s expensive is securing it from robbers that could disrupt the service and tank the value of the coins. Operator outsources this task to Miners&co. They make the train secure proportionally to the amount of real money they spend. To compensate them operator pays them with freshly minted coins for securing each train. Since operator intends to emit a predetermined number of coins in total it has to periodically lower Miners&co reward for each train secured.

There’s a risk that the price of the coins won’t grow fast enough and securing trains will get less and less profitable for Miners&co and they will secure trains less and less until train line falls victim to the robbers.

To create a second source of income for Miners&co operator gives them the fees that people bid to be on the next train. Operator is not sure if it will suffice but that’s the best he could come up with.

There’s a surge in coin price and people start to ride trains like mad to sell their coins at places where there are buyers. People outbid themselves to be on the next train to the point that travel becomes uneconomical for casual travelers. Some of the travelers say: “Make the trains larger so we can all fit in for cheap”. Operator could do that at no cost, because running trains of any size is the cheap and easy part.

If the operator decides to make the trains larger he is lowering the amount of coins that people will have to pay to travel and thus lowers income of Miners&co and thus lower the incentive to maintain high security of the trains. Incentive that the operator already wasn’t sure was sufficient to keep Miners&co interested forever. Operator would be taking away profitability from Miners&co and make them worry that he could just take away more of their profitability in the future on a whim. What’s next? Even less fees? Maybe no base reward for securing trains? Maybe fixed or increasing reward that makes coins not scarce anymore and thus less valuable in terms of real money?

If the operator decides to not make the trains larger, he makes the casual travellers that like to travel often with a small amount of coins unhappy, to the point of using other trains and coins altogether. But the operator keeps Miners&co profitable and communicate to them that he doesn’t intend to change any core rules in a way that negatively affects their profitability

Travellers say, if the operator makes the trains larger, and as a result makes travel faster and fees lower then more people will travel and coin will become more valuable offsetting any loss of profitability that Miners&co suffers as a result of larger trains.

But the operator knows that what makes his coins valuable is not that his trains are fast, or large or cheap or used often. What makes coins valuable is that they are in strictly limited supply and that the trains will operate forever secured strongly enough to never get disrupted by robbers. So the operator chooses not to make trains larger because Miners&co profitability and trust must be considered before anything else because security they provide is one of the two necessary things for the coins to be valuable.

Some people are very upset and they make their own train line and coins (which they give to people that own operators coins). Miners&co prefers to secure operators trains more and the new larger ones less. Price of operators coins doesn’t suffer and follows usual curves it previously followed around moments of high interest. Operator can infer from that that he chose correctly.

Will the operator be able to keep trains running safely forever? Nobody knows, because outside of well modeled problems, nobody knows what the future will be. And this train line is the first of its kind. I you think it’s doomed you are free to ride any other. There are so many now that do various things differently. Choose wisely because many of them already died abandoned by Miners&co.