The ability to bring things to the end is not the basic instinct of the individual. It is not necessary to count on that the kid will independently master this useful skill - it is parents who should help in developing strength of will and perseverance. First of all, it is necessary to be convinced of the feasibility of the task. It makes no sense to demand from the three-year-old kid the wonders of fine art, and from the first-grader - impeccable handwriting.
If the goal is rather complicated, it needs to be divided into several easier stages. For example, to assemble a tower-designer in several tiers or "break" a three-dimensional picture-coloring into parts.
After completing each stage, the child should receive positive feedback. Specific and constructive praise will strengthen the faith of the baby in their own abilities.
Do not forget about adequate motivation - theoretical talks about the accomplishments and exploits of great people usually have the opposite effect. It is better to use more understandable algorithms: game, cognitive, competitive.
The most important rule is a benevolent atmosphere. Trusting the child to accomplish the task, it is not worth it to constantly pull, correct and reproach. Independence in the right framework is an excellent training for overcoming difficulties.