How do you know what to take the lead about?

Sure, but I don't lead all of my sessions now by continuing to discuss the past. It was important to share and be heard, but all I can't change what already happened. All I can do is work with the here-and-now, not the past and not the future. I have a tendency to ruminate and dwell on things, so just talking about past stuff is really not helpful to me. Sure, I've finally acknowledged and accepted what happened, and now I can focus on healing rather than suffering by spinning in the same crap ad nauseum (like how hurt I was about the relationship with my ex not working out, three different times, and for months after it was over).

More of my more traumatic issues stem from later in life, and they've come up in session when something has gotten triggered. Some issues I was open about from the get-go, but others took me time (different for each thing). Usually, the issue is my shame about it or even my own refusal to acknowledge something, but unfortunately sweeping those issues under the rug doesn't work long-term and eventually they spill out and affect me again which I then try to bring up in session. There is still something I won't share with my T, but it's not causing me any issues. Other stuff has taken me many months to share.

The longest I've worked with a T, though, has been my current year and a half. Another T I had for a year. So I haven't had the opportunity to wait longer than that. I only ended therapy when I thought I was stable and didn't need therapy, but then somewhere down the line, the same ol' underlying issues started causing me problems, just in a slightly different way than before. Now I realize what those underlying issues are and can focus on them as I continue therapy instead of the eating disorder or the breakup or whatever.

Regarding the past, while some knowledge can be helpful, my T shocked me once by saying "it doesn't really matter why." But when I took a moment to think about it, it's kinda true (with certain issues, of course. not making a blanket statement). The original why of the issue mattered when it happened, but now I'm continuing the self-hate when that prompting event has long gone. Why I started thinking a certain way or doing a certain thing doesn't really matter right now. I'm not saying to deny or ignore the past, but then it's time to work on the present moment.

My original reply to stopdog came from the mention of not knowing what else to say about it. I just tried to point out that there may not be something else to say about it right now. It may be more helpful for stopdog to focus on what is desired from therapy rather than getting stuck on describing the issue (presumably stemming from the past). I hope I'm making sense, seekingzen.