How do I get better at complex tax planning?

You have already come a long way. You can plan for most situations now, and the fact that the hardest cases still trip you is not a sign you are behind. It is a sign you have reached the part where the real skill lives. Complex strategy feels different because there is no single right answer to look up. It asks you to hold many moving pieces at once and judge, not just recall. That judgment is built slowly, case by case, usually beside someone who has done it longer than you. So stop trying to master it all at once. The next time a high stakes situation lands, do not aim to solve it alone. Walk through it with a mentor and ask them to think out loud. You are not there to have the answer yet. You are there to watch how a seasoned mind moves, and to borrow that shape until it becomes your own.