I've written about why systems are better than goals before, but one of the main benefits is that you don't get so disheartened when you "fall behind." This disheartened feeling many get when the fall behind schedule can lead to an all out meltdown that destroys any progress you had previously made.
For example, let's say your goal was to lose 20 pounds in four months. For the first two months, you're on pace. You've lost 10 pounds and are feeling good about yourself. Then, you have a really bad week and gain five pounds back. Now all of a sudden, you're only a quarter of the way to your goal yet have burned half of the time you (arbitrarily) allotted.
The two reactions to this that seem to be common are 1) Meltdown. Pig out on pizza, soda and bonbons because all is lost. Now, after dieting for two months, you actually weigh more than when you started. Or 2) Go for some crash diet to make up for lost time. This rarely ends well and will, more often than not, eventually become the first option.
On the other hand, if you set up systems to live healthily, you don't have to worry about hitting those artificial timelines. For example, such systems could include; no eating out on your own, no buying junk food at the grocery store, working out four times a week, no eating after dinner, etc.
And this doesn't even get into one of the biggest problems with goals; what happens when you succeed? Do you set a new goal and move back into what Scott Adams calls "presuccess failure?" That doesn't sound like a fun place to permanently live in?
Goals can be useful, but they're not a good way to organize your life. Goals pretty much make you damned if you do and damned if you don't. Systems over goals any day of the week!
"Every day is a new life to the wise man."
The Righteous Mind
Star Slate Codex
Consulting by RPM