For what it's worth I had already observed this effect. I am less likely to carry on with some plan if I talk about it to other people. Now I tend to just do what I have to, and only talk about it once it's done.

Part of the problem is I hate feeling pressured into doing something. Social commitment will, if anything, simply make me want to run away from what I just implicitly promised I'd do. Perhaps because I can never be sure whether I can achieve something : if I fail silently and nobody knows, it's ok. Less so if I told people about it. It feels better to run away from something (failing by choice) than failing for other reasons.

Also in some cases, just saying you plan to do something already feels like you've done something. Either because you count it as a step towards doing the whole thing (a step after which it feels more acceptable to take a break, which can last indefinitely long), either because you fantasized about it enough that you don't feel the need to implement it for real anymore.