Using lookups and searching in Salesforce page layout
When you click the lookup icon without entering a search string, the Lookup window appears with the recently visited records. All records are not displayed in the Lookup window. Salesforce displays the recently visited records to improve performance and speed up data retrieval. You can view all records by clicking the Show all results link.
The following table lists additional information about lookups:
Tip: For faster searching, add an asterisk to the end of your partial query. Example: cert*