I have heard that by telling people about my goals I am more likely to achieve them. Is this true?
Telling someone your goal makes it less likely to happen. This is because the social satisfaction of telling your goal substitutes for the satisfaction of achieving it.
Kurt Lewin, father of social psychology, called this phenomenon "substitution" in 1923.
Gollwitzer wrote a book about this in 1982 and more recently published some tests about it. 163 people in 4 tests, wrote down their goal. Then, half announced their goal to the room, and half said nothing. Then, they were given 45 minutes of work toward achieving their goal, but told they could stop at any time. Those who had said nothing, worked the full 45 minutes, and at the end still felt they had a long way to go. Those who announced their goal, worked 33 minutes on average, and felt they had gotten a long way to achieving it.
"Substitution" is now a well known psychological effect: when you announce your goals to people, you receive psychological satisfaction, and it makes it less likely you achieve them. If you walk around telling friends "I'm going to lose 80 lbs", this makes it less likely you will lose it. If you must tell them something, tell them what you've already done: "I have lost 10 lbs" but don't talk about your goal (although you should certainly have one).
There's no two ways about this: when someone says "My goal is to lose 80 lbs and it starts today! Hold me to it" that act alone makes it less likely they will succeed.
This TED talk goes into this topic in more detail