Friendship is the only thing in the world concerning the usefulness of which all mankind are agreed.

People disagree about nearly everything: money, religion, how to raise children, what a good life looks like. On the value of having a few people genuinely on your side, there is no argument anywhere. That near-unanimity hints at how central it is, and how easily it still gets crowded out, since friendship is the one thing with no deadline attached to it.

Think of who you would call at two in the morning, then of when you last spoke to them. Send the message you have been meaning to send for months. Nothing else on your list has that much agreement behind it.