Don't tell your friends
Andy Weir is one of my favourite writers. I have read most of his books. However he claims he doesn't like the writing process.
I listened to his interview with Adam Grant all about this and one quote in particular stood out. From about 26m29s in he talks about:
Resist the urge to tell your friends and family your story. Most of us, me certainly, are driven by a desire for other people to experience the story. If you tell your story to your friends and family, which can also be difficult when they are explicitly interested in asking you, oh, tell me more. Tell me where that sounds cool. Then it satisfies your need for an audience and it saps your will to actually write it. So the best way to combat that is to make a rule for yourself saying like, no one can experience this story in any way other than reading it. So I've got to write it. So you can still give it to your friends like a chapter at a time so you can get that incremental validation that you crave, but don't just verbally tell them the idea.
I think there could be an element of this as well with developing side projects. It is very easy for you to share the idea and they either say it is rubbish or sing it's praises. Maybe it is better to force yourself to just show them progress rather than discussing it.