One piece of advice I always give young writers is to just sit down at the keyboard and write. Never give in, I advise, to the eternal temptation to leave something unwritten, rather than risk write it badly.

It won’t be as good as you want it to be, I tell them; it seldom is. Write it anyway. I consider this advice so essential that I put it in the first chapter of the book I wrote on learning to fail gracefully.

Advice is always easier to give than to take, of course. I find that I’ve been putting off writing something all week, because I know that it will fail to do justice to its subject.

So: Mark A. R. Kleiman. Notable public policy scholar, “pot czar” of Washington state and first-class human being. Mark was one of the most brilliant and creative thinkers I ever met. He was also my friend. Last weekend, we lost him to the complications of a kidney transplant.

As I write this, I’m remembering that Mark was one of the first readers of my book draft. He gave his time gladly and sharpened my arguments considerably. This leaves me no excuse at all; I am going to fail to convey how remarkable he was, and I am obligated to try anyway.

Others have covered the highlights of his career, so I’ll focus on the person. I “met” Mark sometime in 2002, when both of us were blogging. Eventually we became real-life friends, though honestly, the medium hardly mattered; Mark often seemed a creature of nearly pure — heck, relentless — intellect.

In our little corner of the blogosphere, politics was the normal topic of conversation, and Mark and I were about as far apart on most political questions as two people could be. I was a right-libertarian, much more purist than I am now; he was a die-hard Democrat of the hard-liberal variety. That we became friends at all is a testament to Mark’s remarkable sense of fairness: He didn’t care what you were arguing as much as how. The address of his blog — — was a tribute to one of his favorite quotes: “You’re entitled to your own opinion, but not your own facts.”

Mark could be prickly when he thought someone was being intellectually lazy or dishonest, and he didn’t suffer fools gladly; indeed, he didn’t suffer them at all, but instead unleashed verbal cannons, set to “pulverize.” This won him some enemies, as any accounting of the man has to admit. He simply had no tolerance, or talent, for the casual hypocrisy that lubricates most social interaction.

I think of the time I watched him serve as the respondent for a not-very-good-book on drug policy. This is usually a genteel sparring match; Mark turned it into a blood duel, from which his opponent staggered away, ashen and dazed. Afterward, he looked at me with a twinkle in his eye, but also with some genuine regret plucking at the corners of his lips.

He said, “Do you think I was too harsh?”

“Perhaps a bit,” I allowed.

“I thought so,” he sighed. “But it was such a bad book.”

The qualities that won Mark his enemies also secured him his friends; he was a righteous man in all senses of those words. In 17 years, I never once saw him go along with the crowd when he thought the crowd was wrong, and if he thought the crowd was being unjust to someone else, he leaped into the scrum to stand on the right side, even if that only made for an army of two. He often defended me from angry co-partisans, who predictably turned their anger on him. But I also saw him extend that charity to perfect strangers, never first counting the personal cost.

But then, Mark never seemed to count those kinds of costs about anything. Everyone who knew him has a story about his unstinting generosity; mine is when I sent an email asking him about Hawaii’s innovative probation program, and awoke from a nap a few hours later to a neatly organized list of contacts, the numerous emails he’d sent on my behalf and a background briefing that stretched for pages. Or the time Mark told me he was going to have dinner with Nobel laureate Thomas Schelling. Naturally I expressed some good-natured envy, and the next thing I knew, Mark had gotten on his phone and arranged to bring me along.

When he died, a mutual friend wrote to me that Mark “had no intellectual guardrails”; he bravely went wherever the data took him. He had no social guardrails, either; he had no guardrails. And consequently, as long as I knew him, he always went as far as his mind could go, which is not something that many people can say.

What’s more, wherever he went, he took his friends with him. Dear God, how we will miss that journey.