ommunication problem
Usually it happens if there is no complete understanding of subject of presentation, leads to lack of confidence. Also while presetation, needs proper & specific words to stress the specific point, this will be obtained by regularly reading novels and using such words in day to day life. This will improve the communication skill.
Further If we are expert in reading the audience mind & judge what is they are finding in presentation, & if the efforts made to produce the required, then the presentation is 100% successful.