Databases may be subject specific. For example, if you are looking up an article on computer engineering you don't want to be in a database about U.S. History.
Each database contains different pieces of information so it's important to check a few of them. Think of it like this: Netflix, Amazon, and Hulu all have different shows. Each database is like a different streaming service, except instead of movies & tv, they have journals. You may get different results, possibly some that are more helpful, by searching in multiple places.