The first time I came across keeping a diary of accomplishments was from an entry in the Life's Little Instruction booklet by H Jackson Brown. This was a very long time ago, and I had forgotten about it.
Julia Evans wrote about keeping a brag document in 2019.
Brad Shively recently talked about keeping a Yayme file.
Gregor Ojstersek has a newsletter post about it.
A few years ago, Sriram, my manager at the time, had mentioned keeping a brag document to me. One interesting suggestion he had was to keep note of acknowledgments or compliments received, too.
For example, if you suggest an idea or make a point that was acknowledged or applauded by a senior member, tech lead, or architect, you want to note it down in your document. Keeping notes like this will help build your confidence.
Along similar lines as above, I have also created a document called Learnings. Here, I reflect on things that went well, my failures, advice, and feedback that I have received. This helps in two ways:
The writing helps crystallize my thoughts and I can go back and review for patterns.
When I have received constructive feedback or have made a mistake, writing helps me reduce anxiety, calm down, detach, and be objective.