I have no idea who it was that said the original quote, substituting "necessity" in the place of "dissatisfaction." I suppose that necessity does translate to dissatisfaction with one's state in one way or another, but I think that the whole premise can be broadened to include just simply not being content as opposed to only involving the things we find we cannot live without, even though we cannot have them, and therefore, we must find another means to supply what is necessary.
Perhaps it is because dissatisfaction doesn't always translate to action on one's own behalf that the replacement of that word in the original quote doesn't really apply. I know many people who are dissatisfied in one way or another, be it in employment or in one's personal life, for example, who have no drive or intention to change that. To be honest, I have always had a difficult time completely understanding that. I have met people who are either unable to identify the cause of their dissatisfaction or able to do so and yet, unable to change it. However, "able" presents a funny concept. In theory, we are all able to do whatever we need to in order to make our lives better. I have seen few instances where someone was truly unable, because of causes outside of his or her own control, to change his or her life, especially if he or she knew something needed to change in the first place.
Habit is, I believe, the number one impediment. It's been this way or I've been this way for this long--why go through the struggle? At least I can give people who see it this way credit for acknowledging that change in one's life is a difficult thing to accomplish and will ultimately affect multiple parts of who they are. However, habit is powerful--at least we know what to expect with habit. We can wake up in the morning, go through our days, and then go to bed without a great deal of reflection and most importantly, without struggling. Change is a struggle--it's an uphill battle with no guarantee of success. If you take the risk to change, you may indeed end up worse off than you were before, which will subsequently require more change and more struggle. No wonder so many people are afraid of it.
I never liked the idea of habit. There have been too many instances where habit did not translate into happiness--instead, it led to more dissatisfaction. I do not think that any truly great person, either people who have directly influenced our lives or people who historically have made a difference in this world, accepted dissatisfaction out of hand. Instead, they did something with it. Some of them ended up miserable, yes, but we still remember them anyway. Their ability to deal with dissatisfaction in their own lives and not settle for less is what makes us list their names and describe what they did for us in personal profiles.
Maybe it has to do with how we see life--either as a bunch of "typical" milestones from childhood to school to marriage to kids to retirement, etc., or as one long process that may or may not include those things--but the point being that life, to be fulfilling, does not have to include them. Instead, life could include moments you realized some inner truth instead of marriage or a moment of great accomplishment instead of having children. Although the "typical" can be and is rewarding to a lot of people, it is a guideline, not a set of rules. If that guideline will lead to dissatisfaction born out of habit, perhaps your potential for greatness is what is ultimately at stake.