...so how would corporate banking systems get built?
Although I understand the sentiment, and have followed it with a number of my projects, an aweful lot of companies build and sell software that is not necesarily useful for their own purposes (banking, financial, retail etc).
A better and more general rule, and one that has been stated millions of times is simply its really REALLY important to known and understand your client*.
The client could be a 'normal' Internet user, or could be a multi-million dollar enterprise, but unless you understand them, you can forget trying to get money out of them! (and if they are a multi-million dollar enterprise, the people you need to sell to are very unlikely to be the people that actually use the system and you absolutely do need a mature product strategy and the necesary resources to even make a single sale).
Seems to me that the advice in the OP is intended primarily for someone doing a startup (or planning to). In that circumstance, you're probably not going to stick with such a high risk, even for high potential reward, unless you yourself fit into the group that would use it.
That is to say, you yourself are the client (sort of), meaning there's not so much need to make any effort understand the client, because you already know what you know/how you feel about $THING(/etc.).
Although I understand the sentiment, and have followed it with a number of my projects, an aweful lot of companies build and sell software that is not necesarily useful for their own purposes (banking, financial, retail etc).
A better and more general rule, and one that has been stated millions of times is simply its really REALLY important to known and understand your client*.
The client could be a 'normal' Internet user, or could be a multi-million dollar enterprise, but unless you understand them, you can forget trying to get money out of them! (and if they are a multi-million dollar enterprise, the people you need to sell to are very unlikely to be the people that actually use the system and you absolutely do need a mature product strategy and the necesary resources to even make a single sale).