user133967: For example, if someone was running a full node and somehow re-wrote the software so that blocks and transactions which did not abide by Bitcoin's consensus rules would be able to be relayed, what would stop these blocks from joining the Blockchain?
Is it the fact that these blocks are broadcasted to other nodes that stops the invalid block from joining. For instance, if the invalid block is relayed to a non-corrupt full node and this full node rejects it, then it won't be added <-- is this true?

user13866: Other nodes would not relay or accept invalid blocks that were produced by the modified node.
Each node creates their own copy of the blockchain. Each node checks (verifies/validates) all the data it receives to the fullest extent possible. No node trusts any other node. It is because each node applies the same set of rules that they all end up with the same data in their copy of the blockchain. Nodes that apply different rules end up forming a separate "forked" network with a different "forked" blockchain.

133967: <p>For example, if someone was running a full node and somehow re-wrote the software so that blocks and transactions which did not abide by Bitcoin's consensus rules would be able to be relayed, what would stop these blocks from joining the Blockchain?</p>
<p><strong>Is it the fact that these blocks are broadcasted to other nodes that stops the invalid block from joining. For instance, if the invalid block is relayed to a non-corrupt full node and this full node rejects it, then it won't be added &lt;-- is this true?</strong></p>
 13866: <p>Other nodes would not relay or accept invalid blocks that were produced by the modified node.</p>
<p>Each node creates their own copy of the blockchain. Each node checks (verifies/validates) all the data it receives to the fullest extent possible. No node trusts any other node. It is because each node applies the same set of rules that they all end up with the same data in their copy of the blockchain. Nodes that apply different rules end up forming a separate &quot;forked&quot; network with a different &quot;forked&quot; blockchain.</p>
