There's a certain mass and size of plutonium that you need to create in order to start a nuclear reaction… a reaction that tips, that spreads, that cycles out of control.
In the idea business, critical mass is the minimum size of the excited audience that leads to a wildfire. People start embracing your idea because, "everyone else is…"
For every idea that spreads, it turns out that the critical mass is different. For example, if I want to start a yo-yo craze at the local elementary school, critical mass might be as small as a dozen of the right kids yo-yo-ing during lunch. In an environment that small and tightly knit, it's sufficient.
On the other hand, the critical mass for a better word processor is in the gazillions, because the current standard is so deeply entrenched and the addressable market is both huge and loosely knit. The chances that you will launch a new word processor that catches on because everyone else is using it are small indeed.
TED talks don't have to reach nearly the proportions of a typical YouTube video in order to have a significant impact, because the population of curious idea spreaders that watch and spread these talks is small and connected. The same isn't true for a new music video from the musician you manage.
If your idea isn't spreading, one reason might be that it's for too many people. Or it might be because the cohort that appreciates it isn't tightly connected. When you focus on a smaller, more connected group, it's far easier to make an impact.