Suppose I wanted to learn Irish. I could probably do it. I have learned other languages. It is within the realm of possibility. I am sure that it is a beautiful language with interesting texts for me to discover. If this were my priority, I could do it.
But i will not learn irish. I will die without having even tried to. The one thing that is missing is motivation. Since this is about #552 on my list of things that would theoretically be good ideas to do, I will not do it.
What academics do can be extremely difficult. Writing a dissertation is sheer craziness, from the point of view of the average person on the street. Motivation is what makes it easy or difficult, since the number of people smart enough to get a PhD is 100x the number of people who really want it badly enough. What's more, we all know people not smart enough to get a PhD who actually have a PhD. In a way, you have to admire those people even more.
So what is motivation? Wanting it, not in the abstract, but wanting it so much you will do what it takes to get there. I want to wake up tomorrow speaking fluent Irish, but that's pretty meaningless.