In a team, culture is not decided by what is written down. Not by the core values in the annual report, not by the posters on the wall and not by the director's speech at the kickoff. Culture is decided by what happens every day.
A leader is responsible for three things that together shape the culture: what they let pass, what they correct and what they reward. Each of these three is a signal. And teams read signals more sharply than leaders realise.
When unwanted behaviour goes unaddressed, it becomes part of the culture. Not because it is officially accepted. Because in practice it is accepted. To a team the difference between those two is irrelevant. They do what works, not what is said.
The director who does not enforce agreements in the leadership team has a leadership team where agreements are optional. The manager who accepts mediocre work has a team that delivers mediocre work. The founder who never explicitly names top performance has a team that does not know what top performance is.
Strong leadership means you step in fast, stay consistent and make no exceptions. No exceptions for seniors, no exceptions for top performers and no exceptions for hard conversations. The standard holds for everyone, or there is no standard.
The central question is simple and confronting. Does the reality in my team match the standard I say I hold?
If it does not, the responsibility does not sit with the team. It sits with the leader.
What do I have to do?
Stop describing the culture. Start shaping it through your daily choices about what you let pass, correct and reward.
Concretely
Make the real standard visible. Write down which behaviour you see every day in your team. Not what should be there. What is there. Compare that with the standard you say you hold. The gap is your work.
Correct fast, not later. Every correction you postpone loses force. If someone does something on Monday that does not belong and you only name it in a review three months on, you are too late. Correct in the moment or within the day. Then it is maintenance. After that it becomes an incident.
Be consistent, without exceptions. The most dangerous exceptions are the ones for your best people. Top performers who ignore agreements tell everyone else that agreements depend on status. That wipes out the standard in one move. The norm holds for everyone or it holds for nobody.
Name explicitly what is good. Shaping culture is not only correcting. It is also reinforcing. When you see top performance or sharp behaviour, name it. Concretely. By name. In the moment. People need to know what the standard is, not only what sits below it.
Accept that this is your work. Holding the line in your team is not a side task next to your real work. It is your work. If you make no time for it, you are choosing erosion. And erosion does not get repaired in an annual session.
Culture is what happens when nobody is watching. Your standard decides what that is.
Your action for the next three days
Pick three behaviours you want to see in your team and three you will no longer tolerate. Concrete, specific, without vagueness. Over the next three days, correct every time you see behaviour from the second list. Name it every time you see behaviour from the first list. Notice how fast the team registers the shift.