What is the exact principle behind this technique? Isn’t the transaction once broadcasted is captured with the nodes and it permanently sits there?
It does but it needs at least 1 confirmation. But here again one can also reverse the coin after a confirmation but it will cost you so much power and resources that if this is not huge amount of money then it is not worth it. Once a transaction gets 6 confirmation then you are looking at million dollar expense to reverse the transaction which is does not simply make sense to spend.
For small amount it is advisable to wait for at least one confirmation and for big amount waiting for 6 confirmation is safe.