IRCTC Calendar Design
IRCTC.co.in is the Indian Railways’ ticketing website.

April has only 30 days. I still went ahead and selected 31st April and hit ‘Find Trains’. Guess what happened next?

If you know April has only 30 days why would you add 31st to it? Better than designing accurate error messages, is preventing errors. IRCTC seemed to have missed that part.
Recommended Books on Usability
write to me: sumank [at] gmail [dot] com
You are cool dumbass to select april 31st.