Discipline Early, or Discipline Often - 4 steps to start enforcing the rules

“What we permit, we promote. What we allow, we encourage.” 

Ask any coach if they promote or encourage a player being late to practice and they’ll think your question absurd.
But watch as they shout an annoyed, “Hurry up” to the kid still tying their shoes on the sideline before jogging over to the huddle, and what you have is an unconscious acknowledgment that it’s okay to be a little bit behind.
Perhaps two days pass before another player is a few minutes later, this time joining the team as warm-ups begin. But this individual is a senior starter who was likely getting treatment in the athletic training room, so the Coach says nothing as they join their teammates.
Bit by bit things begin to accumulate until one day, a freshman arrives late to practice and by now Coach has had it. “That’s it. Everybody on the line!”
Players regularly on time are pissed that the rules weren’t enforced earlier, and players who’ve been allowed to arrive late are confused as to why the hammer has suddenly dropped. Additionally, your poor freshman feels unfairly called out for simply doing what they saw a team leader do last week. 
Despite your best intentions to be a positive coach/teacher/parent/partner, you’ve instead begun the unintentional creation of an environment tainted by frustration, confusion, inconsistency and fear.
I’ve seen this play out hundreds of times and the longer we wait, the worse it gets. I’ll hear people say,“Yeah, but I can’t enforce that rule now. I let it slide this long...we’ll just have to deal with it.”
Incorrect, my friend. You have the ability (and one might argue, the responsibility!) to change at any time. It’s HOW you change that matters.

To that end, may I offer the following 4 steps: Recognize, Restate, Restart, Reinforce. Let’s use the earlier example of a Coach addressing the issue of player tardiness …
1. Recognize - start by recognizing your mistake and admitting it publicly. “I realize that up until now, I’ve allowed people come into practice a bit little late, and that’s my fault.”
2. Restate - the “why”, the purpose behind the boundary you’re about to set or the rule you’re planning to enforce. “We’ve said that we are a team that values punctuality, which is why we created rules regarding timeliness. We understand that we can only work together when we're all present.”
3. Restart – establish a new beginning for all involved. “From here on out, if someone is late, [insert pre-determined individual or team consequence here]."  Note: It’s often helpful to define any exceptions to the rule during this step. Life is unpredictable, so if it benefits you to leave room for a judgment call in extenuating circumstances, do so here.
4. Reinforce – the consequence for violating the boundary or rule every time it’s broken. EverySingleTime. I can promise you that your team/students/children/partner will never remember how many times you enforce the rules, but they will always remember that one time you didn’t.

It's never too late to start now ;) Good luck, and let's chat if you could use help practicing the 4 R's in relation to a situation you're experiencing.