This is great advice. I've kept a journal for almost a decade now and it's definitely improved my career especially as I've become more senior.
The comments on HN appear to be missing the point though. Most of the commentors note that keeping a lab book helps them keep a record of what work they've done and how they made decisions. It's a tool to reference later. That's not at all how I use my journal. I almost never review old journal entries.
Instead, I use journaling to help me work through unresolved problems. For example, I might take an hour in the morning to pull apart why a difficult meeting went off the rails or what my next actions should be on a difficult project. Journaling is a tool for self-reflection and self-improvement.
Journaling is also great for helping me break free from inertia. Being effective mostly boils down to working on the right project. If I don't take a break to step back and review my progress, I often end up working on a project because I was working on it last week. This prioritization-by-inertia is a crummy way to choose work.
There's a cultural inertia too. For example, it's really easy to get distracted by a fire-drill that's getting a lot of attention. It can be really easy to dedicate a couple of days to the urgent work. However - I find the urgent work isn't always that important. Journaling can help me identify unimportant work as unimportant. You can drive a lot of value by being the cool head in the middle of a fire-drill.