How to follow up after a networking event

The problem is not motivation
You leave a good event genuinely meaning to reach three people. By the time the week starts you have a first name with no last name, a company you half remember, and a business card in a coat pocket. The intention survived. The information did not. Almost every failed follow up looks like this, which is why advice about being more disciplined tends not to help.
Write the reason down, not the person
A name on its own is useless a week later. What you need is the reason you wanted to talk again. She is hiring a designer in spring. He runs the same stack and has opinions about it. That sentence is the whole value of the conversation, and it is the first thing you forget. Write it while you are still in the room, even badly.
Be specific and be quick
A message that refers to something you actually discussed will almost always get a reply. A message that could have been sent to anyone in the room usually will not. Speed matters for the same reason: you are competing with the reader's own fading memory of you, and that fades on the same curve yours does.
Fix it for the whole room at once
Everything above is individual discipline, and individual discipline does not scale to a room of fifty. The version that scales is a directory of everyone who attended, so that finding someone later is a search rather than an act of memory. Intro Connect keeps that directory live after the night ends, with photos, roles, and private notes only you can see.