eine Schwalbe macht noch keinen Sommer
German
Etymology
Literally, “one swallow makes not even one summer”, a calque of Ancient Greek μία χελιδὼν ἔαρ οὐ ποιεῖ (mía khelidṑn éar ou poieî, “one swallow does not a spring make”). The reference to summer instead of spring is shared across European languages; see the descendants at the Ancient Greek entry for more.