Principle of oscillator circuit

The schematic on the cover of this book is a principle diagram of a Colpitts oscillation circuit.
Can you see why this circuit oscillates?
This book explains how this circuit works and oscillates in an intuitive way.
The oscillation waveform is a sine wave.
The reason why the oscillation waveform is a sine wave is explained so that it can be understood intuitively.
Crystal oscillation circuits and overtone crystal oscillation circuits will also be explained.
If you read this book before learning how to design oscillation circuits, you will learn smoothly.