How do I find peace by focusing only on what I can control?

You have found the line where peace lives: you pour yourself into what is yours to control and release the rest. That is the whole of it, and living there rather than just understanding it is a quiet kind of mastery. Hold on to it, because the world will keep testing it. The strength of this way is that it puts your peace back in your own hands. Outcomes will still swing, people will still surprise you, luck will still turn, but none of that owns you anymore, because you have staked yourself only on what you can actually govern, your effort, your choices, your character. Those, no one can take. The practice now is simply to keep the line clear when things get loud. In a stressful moment, ask what here is mine and what is not, give the first everything, and let the second go. You already know this works. This is just the ongoing, daily art of staying home in the one place your peace is safe.