blockchain – a blockchain validated transaction validated by a single node?

In line with my comment, I’ll try to provide a general, short answer anyway: @Preet has already provided good information. So the bitcoin network is made up of miners (who also run full node), and thousands of full nodes that don’t run mining software. Miners have only one task, to ensure that valid transactions are assembled in a new block. When the block is sent to the network, each full node checks this block, to make sure the miner did not misbehave (provided there is a defective tx).

The full node would check the block and all tx inside, based on these rules. You may also read about protocol rules on this web page. This second set of full goal checks is required, for consistency. Two main reasons come to my mind: as a trader, I want to know, that the blockchain only has a valid tx, and if a miner sends incorrect blocks, its IP address will be added to the list of misconduct guests, and eventually get banned (no more tx being sent to this host). If a misconduct miner does not receive tx, he is out of business, losing all his investment in mining hardware.

Here’s one of the most important things to understand in the concept of bitcoin: it’s more beneficial to play the game, like trying to play against the system.