Meaning: This sentence means that if a talented person is lazy, someone with less talent but who has courage and determination can achieve more.
Choice of Words: Guts means courage and determination. Overpower means to defeat or win a competition. Talent means a natural ability to do something well. Idle means to be lazy or inactive. When you put them together, "Guts overpowers talent when talent idles" means that courage and determination can overcome natural talent if the talented person is not working hard.