The key philosophy underpinning Kim Scott's simple yet pragmatic concept of Radical Candor is care personally while challenging directly. At its core, being radically candid means you offer guidance and feedback that’s both kind and clear, specific and sincere.
I personally don't like the term (sounds like something to be survived!), instead preferring Kim's revised reference to "compassionate candour". If you describe compassion as empathy plus action, compassionate candour engages the heart (care personally) and the mind (challenge directly).
No matter which term you choose, the principle is the same: I'd like to know I have spinach in my teeth before I make a presentation, but please take me to one side and whisper it!
For a quick guide to Radical Candor without reading the book, the useful and entertaining Radical Candor podcast is worth a listen. Kim and her guests share what's worked and what's not over the course of their leadership journeys, plus provide top tips tested over many years of trial and error.