Welcome to the club! Great question. There are any number of reasons why we may be unable to achieve a goal by the deadline. Your instincts are on the mark. When you find yourself in a situation where you are unable to achieve your goal by the initial date you set for yourself, revisit the goal. If it is a big goal, break the goal down into smaller goals and set deadlines that are realistic to achieve.
Step 2: Affirm: I attract success and abundance into my life because that is who I am. This puts you into vibratory harmony with your Source. Your goal is to eliminate any distance between what you desire and that from which you pull it into your life. Abundance and success aren't out there waiting to show up for you. You are already it, and the Source can only provide you with what it is, and, consequently, what you are already.
When you set goals for yourself, it is important that they motivate you: this means making sure that they are important to you, and that there is value in achieving them. If you have little interest in the outcome, or they are irrelevant given the larger picture, then the chances of you putting in the work to make them happen are slim. Motivation is key to achieving goals.
In How to Join the Ranks of Goal Setting Achievers Paul Shearstone writes, "Setting goals is the genesis from which all things great and not so great are accomplished... It should be noted that there is no small coincidence between the one percent that write goals down and the highest achieving, highest income-earning men and women around the world."
Step 7: Monitor your emotions as a guidance system for your connection to the universal mind of intention. Strong emotions such as passion and bliss are indications that you're connected to Spirit, or inspired, if you will. When you're inspired, you activate dormant forces, and the abundance you seek in any form comes streaming into your life. When you're experiencing low-energy emotions of rage, anger, hatred, anxiety, despair, and the like, that's a clue that while your desires may be strong, they're completely out of sync with the field of intention. Remind yourself in these moments that you want to feel good, and see if you can activate a thought that supports your feeling good.
Third, we need to keep our goals consistent. That is, when setting goals, we need to be sure that none of our goals contradict or undermine each other. The easiest way to do this is to have an overarching plan. Working through my Business Planning Makeover, for instance, will show you how to create a framework of business goals by creating an action plan to move your business ahead.

Achieving complex and difficult goals requires focus, long-term diligence and effort (see Goal pursuit). Success in any field requires forgoing excuses and justifications for poor performance or lack of adequate planning; in short, success requires emotional maturity. The measure of belief that people have in their ability to achieve a personal goal also affects that achievement.