(be) an eye-opener (1) a situation that shows you something surprising that you did not know before; an event, experience, etc. that is surprising and shows you something that you did not already know; an experience from which you learn something surprising or new) — что-л., открывающее человеку глаза на действительное положение вещей; заставить кого-л. посмотреть на что-л. по-новому;|| что-л., вызывающее сильное удивление;

Example 1: Visiting people in prison was a real eye-opener for me. (MM) — открыло мне глаза на...; я вдруг осознал/понял, что...

Example 2: Traveling around India was a real eye-opener for me.

Example 3: This is definitely an eye opener for me and we should give inmates a second chance for there is always a possibility for them to change and become good citizens

2) an eye-opener (a drink in the morning) — глоток спиртного (особ. утром спохмелья) (см. [опохмеляться]