When your designs and paper prototypes come to life on screen is when things get serious. Be prepared to see what you have imagined in a very different way—be prepared to see things that don't work. The faster you realize something's wrong, the quicker you'll get back to the drawing board, and the better your chance of releasing a fun game. This is the idea behind digital prototypes. Put a working software together as soon as possible and iterate as much as you can on it to define and redefine your vision. Unlike paper prototyping, digital prototyping is a necessary step. If you're not prototyping, you are making a mistake. Period.
It might happen that the prototyping phase is skipped, maybe because there's no time, no ...
