Take these two examples into consideration. 

The first person is a real dreamer, he has dozens of new astounding ideas every day and has big goals for himself.  In fact, he changes his goals quickly because there are just too many amazing things to achieve to stick just to one of them. He is reading a lot of self help material and considers himself being a really intelligent person.

On the other hand, we have another man who has only one goal, and the only virtue he has is that he's hard working.  He doesn't intend to change his goal for a long time and is determined to achieve it.  He doesn't read any self help material and he sees himself being fairly average in the terms of intelligence.

Which one of those do you think will succeed?  It has been shown many times that people who are successful in their life's rarely change their goals.  And it's been shown that people who aren't successful often change their goals and rarely show any determination.  See, the thing with goal setting is that it can easily become food for your ego.  Because when you start to set goals to feel good about yourself and not to really start acting on it now it's a lost cause from the very start.

Another problem with goals that's fairly common is that a lot of people set different goals just because they've noticed how much work the first goal really demands.  So, they will rationalize in their minds that the original goal was never for them in the first place but in reality they are just overwhelmed by determination they would need to achieve it.  And it's way simpler to just find another goal, just that you'll be able to stop worrying about the last one.

This is why it's imperative to stick to your goals and only rarely change them because in that moment when you'll feel the urge to change them, you most probably won't be able to see that your mind is playing tricks with you.  Our minds are by nature lazy and we want to use the least energy possible to live.  And as a matter of fact it's only natural to have these things happen to you, but it's your responsibility to notice these "moments of weakness" and don't let yourself to sabotage your own future success.

So choose your goals wisely and really dig deep inside to notice if they are one hundred percent aligned with your core values and your present life purpose.  Doing this will allow you to understand yourself better and to avoid the mistake of choosing goals that won't motivate you enough to be really determined about them.