X1 Professional Client indexes the content of your email, files, attachments and Outlook contacts. When you start entering a search term X1 finds all instances of those terms within the documents and files that have been indexed. Because of this, you may not immediately see how a file or document relates to your term.
If you select the file from the list on the left, a preview of the document will appear in the Preview Pane on the right with the search term(s) highlighted. Take a closer look and you will quickly find that the file contains the search term(s) entered.
Beyond content, the X1 Professional Client also indexes file attributes (file name, subject, etc). X1 will include file attributes in your search results. So, the results you see may not have the search term in the content of the file but in one of the file attributes. Reference the refine columns at the top of the results list for highlighted hits:
Knowledge Base will match indexed items with "knowlege" and "base" contained within their contents.
Newsletter refers to only items with "Newsletter" in the title of the item (folder, document, image, etc.).
DOC narrows down results to only word processing documents.
THIS MONTH will only show items indexed or created within the month.