Darvas was a professional dancer who traded by telegram while touring. The book is short, and half of it is him losing money on tips.
The box
He noticed a rising stock tends to trade within a range for a while, then break to a higher range. He drew boxes around those ranges, bought breakouts to a new box, and placed a stop just under it. If the stock fell back in, he was out.
Why it worked
Not because boxes are magic — because the method forced a trailing stop and removed his opinion from the exit. He called himself a “techno-fundamentalist”: fundamentals to choose the candidates, price to time them.
Your own take goes here — how this compares to how you actually trail stops.