The discipline of doing less, on purpose
People tend to hear "do less" as permission to coast. It isn't. Doing less on purpose is harder than doing more by default, because it requires deciding — clearly, in advance — what you're not going to chase, and then actually holding that line when something tempting shows up.
Most overcommitted lives aren't the result of ambition. They're the result of never saying no long enough to find out what the ambition was actually pointed at. Every extra commitment feels reasonable in isolation. Stacked together, they leave no room for the one or two things that would have actually mattered.
Restraint, done well, isn't passive. It's a decision made early enough that you don't have to keep re-making it under pressure. You pick the few things that are actually yours, and everything else gets a clean, un-guilty no.
A short practice: write down everything currently pulling at your attention. For each one, ask "is this mine to carry, or did I just agree to hold it because someone asked." Keep what's yours. Set the rest down — not later, now.