As you might infer from the title the thesis is that Grit is a very powerful force. My comment in our discussion was that this whole body of social science research and life/career advice comes into conflict with other bodies of advice about cutting one's losses, the value of killing 'failing' projects early, avoiding the trap of sunk costs.
How do we personally know or offer advice to others about whether current difficulties are likely to be overcome by renewed effort and persistence and when do we say it isn't working, try something very different?
The question of when to persist, how long to persist and how to pay the bills while you persist are very personal to me.
In 2000 I and a friend did research and the very beginnings of development on a semantic analysis technique that was notably better than anything we could find at the time including from Google and other search engines. But we couldn't find money fast enough and we both had families to support so we went our separate ways and did other things that were more commercial.
About 7 years later VCs started funding similar technologies. And, somewhere around 2010 to 2013 technology seemed to have caught up to where we were at in 2000.
So should we have persisted? It kind of seems like we should have. But, I have seen enough of life to know that sometimes a group of people have a lot going for them, winning awards, raising funding, rolling out product and still end up running into a roadblock on the way to commercial success that sinks them.