DoigteurFou well said. But there is another side of the coin.
When you memorize opening, even if you dont understand moves .. there is psyhological gain when you are black and your opponent does not know next move and plays some wrong move. You already know you know more than him and pressure is off. You are better out of the opening.

X_Player: you're probably trolling, but in case your not, I do know titled players who don't play e4. Plus, a player can be a good player without being titled. Only a titled fraction of players have titles. Finally, GMs tend to know basically every opening, so you could insert literally any opening and say "well, all the GMs know Y opening, so if you don't you can't be that good". It doesn't help the OP with his issues. He doesn't need to know the Italian Game to improve his chess