Understanding the negative potential form


In this sentence:

> 無用なものを入れると、無用なものしか取り出せない

Which I interpreted literally as

"If you put in useless things, nothing but useless things aren't able to be
taken out."

It seems that a more accurate translation would be something like

"If you put useless things in, you can only get useless things out."

My question here is, wouldn't the translation be more indicative of a regular,
non negated potential inflection as opposed to a potential negative?




しか, which is seen in this sentence, works together with a negative verb
ending. It does not negate the verb, in this case, but strengthens a feeling
of 'you can only do ...'.




しか, which is seen in this sentence, works together with a negative verb
ending. It does not negate the verb, in this case, but strengthens a feeling
of 'you can only do ...'.

