There are three basic things that trust does in the lives of people. It makes social life predictable, it creates a sense of community and it makes it easier for people to work and live together.
First of all, you must have trust in yourself! That is the basis for everything you do in your life. Every decision depends on what level of self confidence a person has. If you are always sure of what you are doing, then other people will notice that and it will also give them some kind of confidence. Such attitude gives people around you an impression that your idea is good and true. Of course in specific cases you must distinguish between possible and impossible, so other persons, who rely on you, won't fall on their faces with you, if you fail. If that happens they may not want to do business with you, because you are a risky person.
Good friends could start to lose trust in you. But you also must not be insecure in everything. People surrounding you will keep in mind that you are doubtful in many situations. And you will not be the person they would like to talk with about something important or count on you in e.g. trouble. The way you communicate also depends on how you trust yourself. If you have a good self confidence then you talk freely and openly. If not, then you are a reserved person, who will not gather the information you need in some circumstances or even in your whole life, because of not enough communication.
I think that it is also dangerous to be a very trustful person. It is important to be there for your friends when they need you to entrust something to you. But on the other...