Certain things can hamper your effectiveness when speaking to people.
Firstly, if you don’t appear to be sure of what you are saying, you may find that your effectiveness at speaking to people is reduced. You will come to learn that confidence is very critical, and that what you say is actually not as important as the confidence with which you say it.
Secondly, if you are not capable of reading the people’s body language, especially with respect to their reactions to what you tell them, you may find your effectiveness being reduced when speaking to people.
Thirdly, if you are unable to listen well to people, you may find your effectiveness as a speaker being reduced. It is only through listening to the people that you can start having an idea as to whether or not they actually have capacity to understand what you are telling them. You may, for instance, be speaking about the merits and demerits of social safety nets, to people who have absolutely no understanding of economics or sociology. You may think that you are impressing them with your knowledge when, in actual fact, they are bored stiff: on account of them lacking the capacity to understand what you are trying to say to them.