I used to work on an ML research team. In addition to what the author mentions, there is an entirely separate issue: whether or not what you're attempting to do is possible with the approach you've chosen. Consider making an iOS app. For the most part, an experienced software engineer can tell you if making a given app is possible, and they'll have a relatively clear idea about the steps required to realize the idea.…
Knowing that depends on your level of understanding the field and the math behind and also experience. If you just know how to make API calls, then it's hard.
What would be problematic if you want to do sentiment analysis for some product reviews? Result is the public perception within a margin of error, you have your data, you know what you want, you know how to get there.