Do you tell people about a surprise you have for them or no cause it’s a suprise

My friends are tick off because I didn’t tell them that I bought them tickets to a concert .i made a picnic and invite then to surprise them with these tickets and they got mad because I didn’t tell them I was doing them but that was the point .like was I wrong for doing this .

Update :I apologize for not letting them know but I did tell them that giving the tickets to them at the picnic was a suprise now both of them leave me on read .