Anyone who has never made a mistake has never tried anything new.
Very few speeches and presentations are perfect. Even with speeches prepared far in advance and practiced over and over again, mistakes can be made. The most professional and most polished speakers and entertainers make mistakes all the time. Unless you are singing the national anthem and forget the words, or make up new lyrics as a number of performers have done, the audience has no idea you made a mistake.
Most of the time when you give a speech or a presentation the audience does not have a prepared copy of your remarks. Therefore they have no idea know what you are going say or when you are going ...