This is (mostly) wrong. Sivers himself seems to have regretted how his talk was interpreted and posted this semi-retraction: https://sivers.org/zipit2

But identity-based goal or not, the conclusion that you make yourself less likely to achieve a goal by telling people about it defies common sense. I mean, here's the peer-reviewed science saying my common sense is wrong -- http://www.psych.nyu.edu/gollwitzer/09_Gollwitzer_Sheeran_Se... -- but this is a psychology paper from 2009 so I'm willing to bet real money on common sense, despite seeing no obvious flaw with the paper.