Ideas take that stuff into account, but "the ability to build and sell the product" are not part of the idea.
For example, I have a friend in the accounting industry. She says that tracking time spent on each client is still a huge pain point. Many firms do it with Excel spreadsheets, and some of them even use email.
I have an idea to solve that problem. I know how to build app, pitch it, and support it.
The obstacle is that I only have that one friend in the accounting industry. I could get her firm to use it, but I don't have any particularly special ability to convince the rest of that antiquated industry to modernize itself.
I learned this same lesson with a restaurant startup years ago. Unless you have very easy access to lots of prospective clients, you should never start a company to target those people.
(I'm talking about B2B above. The situation is a little different for B2C products, which just require tons of capital and a reasonable user-acquisition cost for that type of product.)
There's a reason investors are always talking about "unfair advantage", and that always means people. Being cashflow-positive is a game of pushing down your costs (for acquiring and serving users) and pushing up your per-user revenue.
The two factors that influence those metrics the most are your team and your access to the target market. A great team means that your sales move quicker, your product-development process is shorter, and you need fewer people. Access to your target market means that cash comes in sooner, sales cycles are shorter, and sales are bigger.
So when I say that startups should start with the market, I don't mean someone should say, "X market really needs Y product." I mean someone should say, "I know a bunch of executes in the [X] industry, and I can meet any one of them tomorrow."