I fall into the "Build before talking to customers" trap constantly. Even though I know it's "wrong", it is hard to escape it because of the simple problem of not knowing who to talk to. The article suggests doing a search for potential companies, finding contacts on linkedin, and sending out some emails. But what about experimental technologies or developer tools? I wouldn't expect a lot of success with a slow movin…
Then you have a different problem - you don't have a way to reach target customers.
Even if you build your product, how are you going to build a sales pipeline? Your customers won't hear about your product by themselves - you have to get it to them. Many many companies make products that are good, are actually useful, but they don't know how to build the marketing/sales pipeline that will actually make their products profitable.
And just like validating the product to build - building/validating a sales strategy is usually something you should do before building the product, both because it's harder, and because findings there may change what product you end up building.