"I'll reply properly later"

The meaning-to is sincere. You do intend to reply. If someone asked you on Wednesday whether you were going to answer the message from Tuesday, you'd have said yes, of course, tonight or tomorrow, and you'd have meant it. So it's worth asking why a sincere intention held every day for a fortnight produces nothing.

Piers Steel, in a large review of research on putting things off, pooled hundreds of findings on what predicts it. Among the strongest and most consistent were how unpleasant the task was and how far off its deadline was. Both apply here in a way that's easy to miss. The proper reply isn't unpleasant in itself. What's unpleasant is the standard you've attached to it. A reply that admires the cake, answers October, gives some news back and reads as though you took your time is a small piece of writing, and writing to a standard is aversive in the way a form is aversive, even when you love the person you're writing to. And there's no deadline. A message from a friend never falls due. Nothing happens on day seven. So a task that's mildly unpleasant with no deadline sits at the bottom of every day's list, and every day it's there, the stretch grows and the standard grows with it.

This is the part I want to be plain about, and it's my interpretation. The proper reply isn't a task you haven't done. It's a standard you've set for a task, and standards don't get done. They get postponed until the conditions are right, and the conditions are never right at a bus stop, or on a Wednesday night, or on the Sunday you'd set aside, because on Sunday you're tired. The earlier book It can be done today is about small admin that piles up for the same reason. Messages from friends are the version of that pile that costs the most, because a form doesn't notice when you leave it and a friend does.

Here's the test. Ask what the proper reply would actually contain. Write it down as a list. Cake, October, something about your week, a question back. Then ask how long that takes to write badly. Two minutes. The proper reply, the one that would take twenty and needs a clear head, doesn't exist and never did. It's the two-minute reply with a standard attached that stops you writing it. Take the standard off and the reply is there, and the meaning-to can stop.