https://youtu.be/_HQSydlnOjo?is=WzXghKg6-2QervvY What concept took you much longer to understand than expected? I think there is so much changing all the time... My top 3 is: 1) Aronian s thought about positional understanding and how the memory works I found so interesting... 2) Time Management by Caruana 3) Keeping tension by Keymer