The most complex thing

What is the most complex thing I can think of? "The human heart," I
thought wistfully. But no, I think the heart can be understood. It's
difficult of course, because the heart is desperate. And because a
relationship -- a connecting of two hearts -- doubles the
uncertainties. But some experts, even some laypeople, would argue that
they think they understand at least their own hearts - their motives,
dreams, and thoughts. So is that the MOST complex thing there is?

Maybe global problems are near the top of the list. Like natural
disasters, poverty, war, climate change, and such. Those problems,
individually and collectively, can not be solved without changing
hearts and minds, combined with extraordinary technological advances
that would also be needed. So, I guess, that's the same as saying the
complexity of every heart on earth would have to be added to the
complexity of the earth itself in order to measure the complexity of
these problems.

Maybe though, the most complex thing is one that we haven't even begun
to contemplate. Take the Universe as an example -- it's something
about which which human knowledge has huge gaps in understanding.
Gaps so huge that nobody can say even how huge. Now imagine a time
when all of those gaps are filled, and we come to find out everything
there is to know about the universe. ... It's impossible to imagine,
isn't it? Well for me it is. Maybe the most complex thing is
Imagination.