I have created a custom module with custom fields that we use to enter customer testimonials. The intent is to be able to search in CRM to find all of the records that contain that phrase in this custom field for testimonials. 

Testing the search with various words/phrases that I know are in the testimonial fields I have populated, the search results don't always find those records. 

Can anyone help me understand the capabilities/limits of the search functionality in CRM? Why does it not find my searched terms consistently and reliably? 

Thank you.