Uncertainty is the devaluation of things uncertain when choosing between a sure thing and a risky one. Change almost always involves some degree of uncertainty, which causes people to be less interested in changing.
There are four key ways to reduce uncertainty by lowering the barrier to trial: harness freemium, reduce up-front costs, drive discovery, and make it reversible.
For example, Dropbox grew by giving its service away for free through freemium, while Zappos overcame the uncertainty tax by launching free shipping, reducing the up-front cost. Supermarkets offering free samples or companies with lenient return policies drive discovery and make it reversible.