When you fail to plan, you plan to fail.
One of the most important thing in goal setting is to make sure you differentiate between end goals and mean goals. When setting goals, make sure you set end goals and not mean goals. End goals are the things that you ultimately want to achieve. Mean goals are used as a means to achieve the end goal.
Let's take the common I-want-to-get-rich goal as an example. This is not an end goal but a means goal. This is because what you want is not money, but the things that money can bring you. Things like security, freedom, happiness, experience etc. You don't actually want more numbers in your bank account. You want what you think money is able to give you.
Unfortunately, too many people get caught up in the process of accumulating more money that they end up unhappy and unfulfilled no matter how much dollars they make. It's no wonder that they're unhappy. It's because the goal they focused on is a mean goal, not an end goal.
Here's a familiar story: A young man works in a large corporation, aiming to be the CEO so that he can have the money to live a life of security, freedom and happiness. Works hard for 20 years, finally becomes the CEO. But in doing so, for 20 years he spent most of the time working (no freedom, no time for loved ones), the stress is killing him (unhappy), and it affected his relationship with family members and friends.
So he may have achieved his target, but he sure didn't get his ultimate goal. You definitely do not want to walk down that path.
To set a goal, sacrifice for it and finally achieve it, only to find out too late that it didn't give you what you initially wanted. That is a very bitter pill to swallow.
So whenever you set goals, take your time to do it. Do it thoroughly, think it through. You do not want to get it wrong and see all your future efforts go to waste. Make sure you do not mistake mean goals for end goals.