How do you know when a product transitions to the next stage of the product adoption lifecycle and grabs the majority market's attention?

Many ways to slice this one, but let's look at it inside-out via a launch perspective. A typical launch goal is to drive adoption. Adoption benchmarks will vary across B2B vs B2C businesses. Ultimately, the product you launched has technically crossed into the majority if >50% of you user base has adopted / upgraded / migrated to the new solution. On the pre-sale or new sales front it's a bit tougher to specify, but generally a strong close rate indicating deal efficiency is the right signal for strong market acceptance by the laggards.