Prototyping is a must especially on the game mechanics and to find the fun. It is a moot effort to build out the game until you have refined the game mechanic

Prototyping is a must especially on the game mechanics and to find the fun. It is a moot effort to build out the game until you have refined the game mechanic and the fun aspect. Iterations need to be quick and with as little tech weight as possible. Even in small prototypes you can find fun that you could have never planned for, and see when something you thought would be fun just isn't yet or work with it to make it fun. Finding the fun is the most unknown part of a development so it must be in the playground/sandbox and iterated on quickly. Playtesting is also important but prototyping usually has lots of that from the developer themselves even.