Let's examine the short fragment of the story:

>!  
>! "... **W**hat is that? **A** 3-complete word?" **T**he  
>! puzzle-solver said. "**C**an it really be solved?"  
>! **H**e thought as he tried different codes in   
>! the keyboard to open the door  
>!  
>! **A** voice in the dark answered: "**S**ure! it can  
>! be solved, just identify the pattern in the  
>! words"  
>!   
>! "**Y**ou... you designed the pattern, don't you?"  
>! **O**ur puzzle-solver replied. "no, it was already  
>! designed. **U**se your eyes to find the pattern",  
>! the voice said to him.  
>!   
>! **T**hen, after deeply thinking, he said: "**Y**es!...  
>! it's solved!" **P**romptly, he opened the door  
>! using the code he found. "**E**xcellent! the  
>! pattern was always in my hands", then he left  
>! the room, looking for the next puzzle to solve...  

Maybe you already saw the pattern.

>! Extracting all uppercase letters from the text gives us the phrase  
>! **WATCH AS YOU TYPE**   

Additionally to the answer for this question, we now have another hint for solving [What is a R-complete Word™?][1]

  [1]: https://puzzling.stackexchange.com/questions/87459/what-is-an-r-complete-word