catalyst

something that causes or speeds change

Catalyst keeps a loosen-and-release image: something helps a change start moving faster.

One honest question became the catalyst for a better discussion.

For catalyst, keep one image: a stuck reaction loosens, and change starts moving. Cata-/kata- adds thoroughness; lysis gives loosening or untying.

Chemists later used catalyst for a substance that helps a reaction move faster without being used up in the same way. In ordinary speech, a question, meeting, or person can be the catalyst that makes a change finally start.