It’s now day 18 after the official start date of the 30-Day Challenge. I’ve certainly had some tough days so far, but I haven’t missed a single day yet on any of my three challenges: 1) get up at 5am every morning, 2) write for at least 4 hours per day, and 3) exercise aerobically at least 25 minutes every day.

If you’ve gotten this far, you’re likely to make it to day 30 without quitting. What you may have noticed is that if you have a hard day somewhere beyond day 15, your self-discipline has grown to the point where it doesn’t seem so hard.

An old high school friend of mine is celebrating his 35th birthday in Vegas, so we had dinner last night with some of his family and Harvard buddies on the Strip, and then I taught some of them to play a few casino games. (I tend to only play blackjack and poker, since those are the ones where I can gain an edge. I was kicked out of the Barbary Coast once for card counting.) My friend and I played blackjack together — just like old times, since we used to make a lot of L.A. to Vegas trips in our 20s — and we both won. It’s always a lot more fun when you’re winning.

But I knew I still had to exercise that day, so I ended up going running around midnight, went to bed at 1am, and then got up at 5am and polished off 4 hours of writing by 10:30am the next morning. It was hard, but my capacity for handling “hard” has increased, so I knew that no matter how late I got home, there was zero chance of me not keeping my commitment.

That’s the great thing about self-discipline — when you take the time to develop it, it leads to greater self-trust.