He says at the end what /u/Kattalalakis is saying, telling someone your goal and risking letting them down drives you to do it. Obviously if you tell people you're planning to lose weight and they tell you that you're fine as you are or whatever won't help, but saying I'm going to run the 10k next summer and having them hold you to it will make you likely to train for it.

Besides which the 2009 study is flawed, if you're in a room and people announce stuff they're doing you always feel left behind, working harder and reporting that they feel they've more to do isn't about everyone else feeling they've done more, it's about them feeling they've done less. Heck if you want to achieve something listen to success stories, people who've done what you want to do make you feel more comfident about achieving your goal while also making you feel more willing to work for it so you have your own story to tell one day. It works (and is the reason weight loss groups succeed slightly more than people dieting alone, support plays no part in it, but the same of public weight ins and ability to hear from people who have done what you're doing works).