think straight

to think clearly. (Often negative.) I'm so tired I can't think straight.

to use your mind effectively The actor said she was so surprised to be nominated for an award that she still can't think straight.

Usage notes: usually used in a negative way, as in the example

Name	Pronounced	Usage
Cherish	CHER-ish	English
Ananias	an-ə-NIE-əs (English)	Biblical, Biblical Latin
MÁRcio	-	Portuguese
Ireneusz	ee-re-NE-uwsh	Polish
Justice	['dʒʌstis]
Onisim	-	Russian (Rare)