Caleb Denby shows what can happen when one simply memorizes opening moves without knowing the theoretical ideas behind them. See Anand lose in six moves.

Follow along: https://lichess.org/study/RSchAaZE

2019.02.27
Alonso Zapata vs Viswanathan Anand, Biel-B (1988): C42 Petrov, Nimzovich attack
http://www.chessgames.com/perl/chessg...
Luke Ye (1900 URS) vs. Caleb Denby (2007 URS): B19 Caro-Kann, classical, Spassky variation
Denby vs. Ben Shoykhet (1900 URS): A40 Modern defence