I've always liked to write; when I was much younger, I wrote a lot of poems and short stories. For several years in Junior High and High School I did a periodic "newspaper" for my family.
I don't recall keeping any sort of diary or journal during elementary school or High School. I did keep a regular journal through all four years of College. I can't remember what triggered that, but I wrote in it most every day. I still have the first volume of that journal (discovered recently in a box with my HS yearbooks and a couple of photo scrapbooks). If I still have the remaining volumes, they are stored in a place so safe even I don't know where it is. To be honest, I'm not sure I would want to read those journals if I could find them again. Perhaps they're better off in that "safe place".
The summer of 1981, after I graduated from College, my sister and I took a multi-week trip by train from Pennsylvania to California and I kept a journal of the trip. After that, the journalling seemed to fall off.... perhaps Grad School was simply too busy. I may have kept a journal in the first year or so; I can neither remember nor do I have physical evidence to support the possibility :-) I did write a lot of long letters to several friends during my first (abortive) half-year of Grad School and probably for the next 6 months as I hashed out "What to Do With My Life".
I didn't do any daily journal writing after I met Rich (in '83), although I did keep a trip journal of several long trips we took later, including two trips to Europe in '85 and '87.
I discovered the WWW in 1993 or '94 and created my own set of pages in late '94 or early '95. Most of my creative writing went into "static" web pages until I discovered weblogging in May 2002. For whatever reason, I didn't really get "into it" until Feb 2003, when I installed Moveable Type and started making entries more often.
These days my personal writing is all online and publicly accessible, across 3+ websites and 4 different weblogs. I don't record day-to-day minutia anymore; my everyday life seems less remarkable than it did when I was in College. Oddly, looking back, when I was writing in College I don't think I was writing for "memories" but merely to write, to make the day more real by setting it on paper.
The things I write about today are less personal, more for public consumption (whether or not anyone reads them besides me!). Nevertheless, everything I write is something I think I will want to remember, someday. I write for others, yet I am always writing for me.
I guess my motivation for beginning a journal, way back all these many years ago, is that it gave me a chance to consider and record something very new and different in my life - College. Every day was full of new and interesting (to me, at least) things. Every day was full of ideas, decisions, new paths to take. When I started grad school (especially the first attempt!), long letters to college friends took the place of the journals. After I met Rich, I didn't seem to need either the private journal or the long letters anymore. I had someone to talk to, to tell all the details about my day and to share my life, my plans, and my questions and (in)decisions.
The web has given me a chance to branch out and make contact with more people, to save ideas and thoughts I have, to share with friends and family (and total strangers). I can't really say why I suddenly started "journalling" again, in a different format, a different style, and after a 20+ year hiatus! Obviously the time was right; I'm having a lot of fun.
I'm especially happy to have an online medium. My early journals (except for the family newspaper :-) were all hand written. These days I do much better typing; too much writing by hand causes my hand to cramp.