1. They don't take the time to write down their goals.
2. Another major reason people don't achieve their goal is because of fear.
The secret to conquering fear is to face it. Failure does not kill, it only strengthens and educates. It is simple; if you fall twice, get back up three times. Tackling fear is the most important thing on the road to achievement. You can also get other planning materials like The Fear Hacking Journal to help you conquer your fears.