The second day of the "12 Days of Retool" series focuses on the concept of tuples and their use in JavaScript, despite the language not having tuples as a native data type. The discussion explores how tuples, which are ordered and immutable lists of items in languages like Python, can be mimicked in JavaScript using arrays with semantically meaningful positions, especially for data consistency and performance optimization. The article highlights scenarios where using tuple-like structures in JavaScript is beneficial, such as representing naturally related data or maintaining positional significance, with practical examples provided in React, particularly with state management using hooks like useState in Retool custom components. Additionally, it contrasts this with the state management approach in Retool apps using the "model" object and "modelUpdate" function, demonstrating how to manage state both locally and globally within Retool applications.