Motherhood. I also thought I could do it all, but the time, mental focus and more time that research takes was impossible to find.

I'm with you. Before having DD1, I knew my work would take a hit for a while, but overall I thought it would progress OK in the longer term. In my head, I thought the disruption would only last a year or two. DD1 was a terrible sleeper. I had 3 years of mind-breaking sleep deprivation, which had a huge impact upon my productivity. I never saw that one coming.

Then, just as she was sleeping better, I had DD2. I reasoned that I would be unlucky to get a poor sleeper twice in a row. I was right--she slept so much better. What I didn't see coming was PND and admission to a mother and baby unit. Over the course of a year, this morphed into bipolar. That was ten years ago. Career-wise, I'm on my knees and just hanging onto my job.

Sorry to waffle on . The short answer is--I chose children, thought I could do it all, and realised it was even harder than I could have ever imagined.

I suppose the question is whether you regret making that choice? It makes me very sad that I will never make it to professor and I wish it could have been different;, in the early days I questioned whether I had made the right decision. But I've moved on from that and I would make the same decisions today as I did back then. Although it doesn't stop me mourning the loss of something that was very important to me.

I don't think it's necessarily an either/or, sorry.

For some circumstances, it certainly is. I was promoted to prof while my kids were still small - though kids definitely slowed down progression and it's been a bloody hard slog regardless - but I couldn't have done it if I'd been hit with PND with either pregnancy, or if one of my kids had a disability that needed extra care, or anything else like that.

There was another thread recently about being a mother and an academic. The general impression was that everyone finds it hard and that some (for various reasons, often outside their control) find it impossible.

I'm doing both. However, it's only possible because I have a partner who also works in HE so 'gets it' even though he's not an academic plus we share childcare, chores etc.
It's tough at times though.

It's not an option for everyone, but one option is to be kind of ok at both, but not excelling at either! I am a SL who started their career a bit late and then had kids along the way. I'm not as advanced in my career as some who are professors, but I'm doing fine, and given this is a long long game, I think it's ok to do well later, but also to treat academia like a job rather than a vocation. There will always be people who work longer, harder and more intensively than you, but I've made my peace I'm not them! I'm glad I hung onto my job, perhaps not doing it amazingly, during the small kid years and now they are teenagers it is actually fine being an academic and a mother and I know many of my friends find it fine too. The hardest is the early years especially as so many academic couples prioritise the husband/man's career at this stage, but if you can get through that, I think doing both is doable, for some people at least.