If you really want to reach for a goal make sure you set your goals high enough. It doesn't even matter if you set it unrealistically high and never reach it. That'll keep you going.
But what about accomplishments? If the goal is out of your reach you won't get the satisfaction and revard for completing it. Set milestones, and collect those. Step by step you reach higher towards your goal. And in the end you might surprise yourself.
Setting a goal that you know you can reach is not challenging yourself. So why stop there? Set yourself up for a challenge.
Lets take running for example. If you set a goal to run 10k that's doable in six months. If you however set your aim to a marathon that might take you couple of years. But you might be already running more than 10k after half a year because of more rigorous training.
If you set your original goal lower and then when you reach it decide to carry on setting your nex goal again a bit higher you can reach results. But it will be slower.
And remember: it's not about the end result, it's about the journey.