You conceive of your goal.
You write it down.
You plan out your steps to achieve the goal.
You even take the first step.
Then, it seems inevitable that somewhere along the way, you get off track, you lose motivation and your focus on your bigger picture. The time, commitment, or sacrifice has come into play, the stuff that really tries you. Your slow progress toward your goal and minimal (if any) results further deter your efforts and you eventually give up.
When you were a kid, how did you imagine your life as an adult? Did you want to be a doctor, or a teacher, a firefighter, or maybe even superman/wonder woman? As children, we had a vivid imagination and we believed that the world was our oyster.