Exactly, and fees are only an incentive. There's nothing stopping miners from discarding your transaction. Therefore trust that miners won't discard your transaction is required.
Of course, the concern that some particular miner might just have it out for you to a degree that outweighs this incentive, or who has some other incentive to not include your transaction, is more mitigated when there are more separate/independent miners/pools .
why would the miners discard a transaction and not another one given that the value they extract is the same?