Best thing I have done as an adult. Started in 1990. Inspired by a visit to an old Meeting house in wales caled "The pales" and buying a book called, I think, Diary of a countryman, the journal of a member of that meeting in the 19th Century, the book reprinted a year's worth of entries.
Kept it Daily till around 2001, when the frequency fell off somewhat. Still use it.
basically it is the tool I have used for working out a Lot of personal stuff, interpersonal stuff, the sort of things I don't find intuityive, BUT, given a ood session writing thoughts doesn, sometimes actual question and answer sessions with myself I have been able to crack a fair few intractable situations, in many cases better than Neurotypicals also involved because of the thinking and preparation working things out in the journal gave me.
Most recently it was the place I reviewed a fair bit of life history which had recurring themes pointing towards being on the spectrum, and it proved a useful tool in a two year process leading to being assessed and indeed identified as Autistic.