I just watched a video called 'Speak With Conviction' by an American public speaker named Taylor Mali. He gave a speech about how the newer generation, 'Generation Y,' speaks with an upward inflection at the end of every sentence, as if everything spoken by that person was a question. This technique of speaking evokes a sense of 'uncertainty,' which isn't good if you're trying to exude confidence. For example, if you were being interviewed for a job opportunity, you wouldn't end every statement as a question. He also spoke about putting the word "like" in your sentences unnecessarily. Doing this has the same effect as ending your sentence in an upward inflection. So, basically, his speech was about having more 'conviction' in your mannerisms and evoking confidence by speaking with certainty and authority.