Follow-through is finishing a job. It might mean calling a prospect back after they were given a presentation to ask for a sale. It might mean finishing a project around the house that was started a year ago. It might mean getting around to writing a thank you letter for a gift.
Amazingly, most people are horrible at follow-through. This means that if a person can learn how to follow-through, they have a huge advantage over most people, even the ones who are more talented! This is exciting news for self-determinists!