What Is a Lynchpin Habit?

Identify the things you're choosing to do, and then after that, identify the things that you would notice if you didn't do. And what i mean by this is it plays a pivotal role in the rest of your day. A lynch pin is something that affects everything else around it. So for me, making the bed affects my mind set for the remainder of the day. If i get that one thing done, i feel accomplished,. I go into the rest of the day feeling like i can tackle whatever is thrown at me. Those are important habits but they're not lynch pins. For you,  what is your version of that? What is it that if you