You’ve just signed a lad for £20 million, he’s young and enthusiastic but maybe a bit raw.
The key thing to do is build the players confidence, especially during this tricky period where everything in his life is up in the air - new teamates, new league, new country, new area, new house etc.
So you give him game time - and allow him to make mistakes - to then work on those in the week. You build the foundations with the player by installing the notion you have belief in him and keep playing him.
If he’s in and out of the side - his confidence gets knocked and you can get in a tricky scenario where a creative player is second guessing their decision making; and can get either a player playing ‘safe’ too often OR the opposite of trying too hard to impress and forever going for the killer ball.