The 20-year-old Dutch winger, a £11.5m summer buy from Ajax, said: "Rafa knows everything about me, down to the fine details. Not just about my style of play, but my character too.
"He told me he had watched me play in an away game for Ajax, and it had struck him how easily I was influenced by the crowd.
"He saw how I was struggling when the fans turned against me. He could tell from my body language - I had unknowingly let my shoulders drop.
"But he told me that the abuse ought to make me stronger, saying the more the opposing fans swore at me, the more afraid of me they were."