The narrator talks about their success in getting a promotion and material possessions like a company car, house, and friends praising their achievements, but ultimately realizes that the best thing they had going, presumably a relationship, is gone.

Meaning of "The Best Thing That I Had Goin'" by Brad Paisley

The lyrics seem to emphasize the theme of prioritizing what truly matters in life. Despite the narrator's professional success and material possessions, they come to realize that the most important thing in their life, presumably a love relationship, has slipped away. The song reflects on how sometimes people get caught up in chasing external measures of success, only to later realize that true happiness and fulfillment come from meaningful relationships and connections with loved ones. It serves as a reminder to not lose sight of what truly brings joy and fulfillment in life amidst the pursuit of career aspirations and material possessions.