I watched the 3Blue1Brown video about the blockchain and a question arose.

How is it ever guaranteed that if I send out a broadcast it will ever be put in a block that gets verified. For example it (my transaction) could reach miners who start verifying the block with my transaction but other blocks without my transaction get verified first therefore my block becomes obsolete because the everyone else is on another fork.

It seems like catching a moving train but with the chance that you run at the exact same speed as the train and never can get on it.

  • There is no block until a miner "finishes" "verifying" the block.
    – user253751
    Mar 30, 2021 at 17:19

2 Answers 2


When blocks become stale, transactions in them are returned to the pool.

Transactions in the pool are available for inclusion in a subsequent block on the winning fork.


If there are two competing blocks at the same height (which happens rather infrequently), each node will only consider one of the two the best chaintip. The other block is not part of their best chain, so it is irrelevant what transactions it included. Therefore, the same transaction can be in multiple competing blocks at the same time. If the transaction paid a high enough transaction fee rate, it'll probably be in all of them.

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