Every organization has a culture, so does every family. Culture is the, usually, unspoken beliefs about how things work around here.
Peter Drucker famously said, "Culture eats strategy for breakfast."
Culture is often what enables or prevents an organization from achieving goals.
For example, if an organization sets a goal to increase on time deliveries, but the culture tolerates excuses, it's unlikely that the team will achieve the goal. The company can provide incentives, and it may drive a short-term spike, but in the end, the culture will ultimately prevail.
Why does this happen?
It's a case of implicit versus explicit. Most leaders are explicit about goals, they write them down, share them, and measure against them. But when it comes to culture, it's more implicit. We assume people should just "know" how to behave.