The Search Mindset

Consider your intent when using a search function. I like to think of two possible expectations:

1. Discovery -  finding data and concepts related to search terms. In other words, "I am not sure what is out there. I want to learn more".  Search results typically get wider when showing something like "related concepts" concepts panel. 
2. Refinement - filtering to reduce results according to given search criteria. In other words, "I want to see only related data and concepts. Search results typically get narrower when showing  something like a faceted result.

This may not seem like a big distinction but discovery and refinement generally focus on different outcomes. Mixing both in a single result list can be confusing.  

With that said, the ability to "pivot" and let a user seamlessly switch from "narrowing" to "widening" activities is a critical feature that distinguishes awesome search engines from the also-rans.