Something else can be gained from the first point, and that as a start up, at first, your priority is to get something that you can actually sell and market.
There's no point spending energy marketing or selling something that doesn't exist yet. No point in having a website about it either. Code your product/service first, because without a product/service you can't sell it, and without sales you have no income.
I have to half-disagree with this, you CAN "sell" something that doesn't exist and sometimes it's a good way to test interest and ideas.
You don't want to sell complete vapor (as in get a lot of interest then be like, oops now wait 4-5 months or whatever) but you don't want to build something that nobody wants or realize that people don't want it as badly as you thought they did.
There's no point spending energy marketing or selling something that doesn't exist yet. No point in having a website about it either. Code your product/service first, because without a product/service you can't sell it, and without sales you have no income.