I do love to eavesdrop. It's inspirational not only for subject matter but for actual dialogue the way people talk.
If I didn't try to eavesdrop on every bus ride I take or look for the humor when I go for a walk I would just be depressed all the time.
The first stage in a technology's advance is that it'll fall below a critical price. After it falls below a critical price it will tend if it's successful to rise above a critical mass a penetration.