This happens to me too, and it's doubly worse when I've made a little progress on a project in addition to telling/showing someone.

For example, a couple of days ago, I implemented a 'MVP' for a sweet (my opinion ;) IntelliJ plugin[1], but since telling/showing co-workers I lost the motivation that got me started on it.

[1]: https://github.com/nndi-oss/intellij-gensett