SharePoint search returns no results for most users

There are many reasons that SharePoint search doesn't return results. The simpler ones like the crawl failed, scope not crawled. If you are in a dev environment, it's likely that you suffer from sloppy use of service accounts. What I learned in a hard way recently is that in a new dev envrionment that I spun up, I was using the the farm admin account as the site collection admin on a site collection, and also use it as the crawl account. Using farm admin as the crawl account is not a best practice security wise but is actually done often to avoid many search related headaches. What I did not realize, is that using it as the site collection admin resulted in the search only returns results for this account in the site sollection. Logged in as any other accounts, search would return no results. In fact, the crawler account should only have explicit read permission in a site collection in order for the search results to return properly for any user. Even though the farm admin account has implicit permissions to any site collection, it must not have explicit site collection admin, site owner etc permissions on the site collection.