When building something for a startup the rule of thumb is to use the tools you know best. Your priority is to build something quickly, that you can show to pot

When building something for a startup the rule of thumb is to use the tools you know best. Your priority is to build something quickly, that you can show to potential customers or investors, not to learn a new tool. For that you can do a weekend or side project. Aside from whether it's a good idea to use Drupal or not, why is he using something he doesn't know ?