だけ and しか: expressing limits
だけ and しか can both express a limit, but they require different sentence patterns. Translating the negative after しか in isolation can reverse the intended meaning.
Limit the scope with だけ
水だけ飲みました。 means 'I drank only water.' The range of what was drunk is limited to water, while the verb is affirmative. 水だけを飲みました, with を after だけ, is also possible.
だけ can also occur with a negative, so do not learn it as always requiring an affirmative verb. 私だけではありません。 means 'It is not just me.' Check what is limited and what is being negated.
Read しか with its negative
水しか飲みませんでした。 also means 'I drank only water.' Read しか and the negative together. Interpreting it as not drinking water at all gives the opposite meaning.
千円しかありません。 means that there is only one thousand yen, not more. It can suggest that the amount is insufficient, but it does not always express dissatisfaction. Read the speaker's attitude from the situation.
Check the amount and meaning
十分だけ待ちました。 and 十分しか待ちませんでした。 both limit the waiting time to ten minutes. The negative in the second sentence does not mean the speaker waited for zero minutes.
Practice pairing だけ with an affirmative and しか with a negative while keeping the quantity unchanged. Then describe what actually happened and what was excluded to check the scope of the negative.
Check: Does 千円しかありません。 mean that there is not even one thousand yen?
Show the answer and why
No. It means that there is one thousand yen, but no more. Read しか plus the negative as a single limiting pattern.