A thought of life

"Think before you speak", I have heard this many times by different people: my parents, my friends, and teachers. I think this is a very important life lesson, critical whenever I start a conversation with someone. But by thinking before I speak makes me feel like a deceitful person. Like I can't be honest even in a normal conversation. When I want something from someone, especially when I want him/her to change their habits, it is very difficult to say it in a way that will not hurt their feelings: Because no one wants to be wrong, they generally do not want to question themselves. By telling them in an aggressive way will surely not get anything done. It is a mixture of assertive communication and "invisible" action that will convey the message effectively.