I regularly review a list of Stoic-related questions that ask, among other things, whether I distinguished between things over which I have control and things over which I don't have control. I review this list every day, and most days I find that I was at least somewhat concerned about something over which I had no control. I'm getting better, but this seems to be a deeply ingrained issue, even given regular reflection and ongoing effort. I think it's interesting how much you can benefit from regularly reflecting on a "simple" idea, and how much you can struggle to implement it despite its "simplicity". There's really something to be said for getting the basics down rather than trying to be all fancy.