This is really good advice.
It also ties neatly into the simplest version of the formula for getting people emotionally engaged with your characters: or how to build the moment in which your character starts moving from their initial state to the state in which they'll start changing their own lives.
First, you figure out the one important thing the character believes that they're wrong about. There's usually a core misperception that they haven't examined. Once they're forced to engage with it, it'll start to change everything about their perception of the world they're inhabiting and/or the people in it.
Then, as V.E. says, you identify the character's great desire and their great fear: the thing that character wants more than anything, and the thing or situation that terrifies them, and that they'll go to any lengths to avoid.
And having identified these two objects or situations, you build a situation in which the two forces will be in close, direct opposition to one another... then drop the character down in between them, and squeeze. Those two opposing forces become the jaws of a vise... and you crank the vise more and more tightly closed until the character has no choice but to acknowledge those opposing forces, and start (even in a small way) to deal with the pressure being exerted and push their way through.
This does not have to be, initially, a great climactic moment. In fact, it works better if it's not. It's more effective if your character has a brief low-intensity brush with these conditions-in-conflict early on. That way, when your big resolution scene comes along about two-thirds or three-quarters of the way along through the story arc, you'll have set up a resonance between that earlier hint or intimation of what's to come, and the really big blowoff. Your readers will recognize the resonance—the throb of tension between the two occurrences, like the vibration of a plucked string—and will find satisfaction both in the true resolution having been partially telegraphed earlier, and in how it's now being experienced and resolved in full.
This approach also allows you to set up more minor resonances between the realization of the conflict and its final resolution. These can serve to bind the structure of the work more closely together: to make it look (and be) less like a series of loosely strung-together plot events, and more like a unified whole, in which ripples of story business flow backwards and forwards, interpenetrating and influencing one another, and hinting at the big one to come.
But none of this can happen until the paired and opposing what-do-they-most-desire, what-do-they-most-fear axes have been defined. So that's a subject it's smart to spend some while thinking about (and for all your characters, not just the major ones), to be sure you're getting it right.
It's not unusual to get the wrong answers, or merely superficial ones, while you're still working out what's actually going on with the characters. So take your time. Eventually you'll find a set of answers that feel unquestionably right... and you can then nail those down in your notes and get on with making the kind of "good trouble" for your characters that will see them made complete.
