While many players will have set goals for themselves before starting on the path to riches, an unfortunate number of players start making gold with the sole aim to be "rich." I, however, have some news for you; you'll never be rich enough, and there will always be somebody out there richer than you. Not setting yourself clear goals can lead to burnout and your premature exit from the gold-making world.
Here are some examples of goals you can work towards and then expand your horizons from there:
Buy a Grand Expedition Yak
Get a hundred thousand gold in your pocket
Participate in a Gold DKP run (more on this in Chapter 2, Earning Your First Gold)
Acquire a million gold
When it comes to gold-making, the sky is the limit for the goals you can set for yourself. As the game progresses and more content is released, not only do more and more big-ticket items get added to the game, but also more gold gets added to the economy, devaluing the gold you've already made.
The reason for setting goals for yourself is that goals give you an end-game; they create a finish line in an otherwise endless race to riches. Clear, defined goals keep the end in sight and can keep you from burning out. Start with smaller goals and build your way up from there. You should keep setting new goals for yourself even if you're comfortable with the original one; you don't need to stop at the first goal.
This, however, doesn't mean that you have to think of gold-making as a job; in fact, the most successful of gold makers are the ones who simply love the rush of a big windfall, lording over giant metaphorical piles of gold and trying to stay ahead of their competitors.