I'm sure there is a 'rational' [='sensible, reasonable'] explanation for his decision.
Humans are 'rational' beings. [=are able to use reason when thinking about something]
No 'rational' [='sane'] person would behave like that.
(..) Dialogue: Marked=..,Default,NTP,!Effect,Miss Granger? Dialogue: Marked=..,Default,NTP,!Effect,Be that as it may, it was\Nan extremely foolish thing to do. Dialogue: Marked=..,Default,NTP,!Effect,l would've expected more rational behavior\Non your part and am very disappointed in you, Ms. Granger. (..)2001 Harry Potter and the Sorcerer's Stone