What is meant by 20% of time on Training Wheels?

By Twenty percent of time on Training Wheels , Daniel Pink in his book Drive means that companies like Google , Atlassian in the modern age of innovation and creativity encourage their employees to devote 20% of their total time to do something of their own in order to create a shippable product.

This is the result because of which Google gave birth to Gmail and Google News and is regarded as a pre-requisite in the modern age of Motivation 3.0 where autonomy is a key ingredient to nurture mastery in modern day knowledge workers.

Adopted from Daniel Pink’s book Drive