I think both you and the author are kind of dancing around this point:
It's fine to choose a large market, as long as you niche down your specific offering with a differentiating factor specific to that niche which, in effect, shrinks your market.
A solo biz can't reasonably compete with Salesforce in the "B2B CRM" market. But a solo biz can prosper in the "B2B CRM for personal injury law offices with < 10 employees in the US", as a totally made up example.
It's fine to choose a large market, as long as you niche down your specific offering with a differentiating factor specific to that niche which, in effect, shrinks your market.
A solo biz can't reasonably compete with Salesforce in the "B2B CRM" market. But a solo biz can prosper in the "B2B CRM for personal injury law offices with < 10 employees in the US", as a totally made up example.