Arteta dropped England goalkeeper Aaron Ramsdale for his August signing on Sunday.
He later explained: "The same rationale that Fabio played here or that Eddie played ahead of Gabriel Jesus. I haven't had a single question on why Gabriel hasn't started - he has won more trophies including me in that dressing room but they don't [ask why]. It is something that historically is done like this but I cannot have two players in this position and not play them. David has tremendous qualities like Aaron has and Karl has, but we have to use them and it is like this.
"I am a really young manager, I have only had three and a half years in the job and I have few regrets. It was on two occasions, that after 60 minutes and at 85 minutes in two games in this period I could have changed the keeper in that moment, and I didn't do it. I didn't have the courage to do it, but I am able to take a winger or a striker and put a central defender at the back to make a back five and hold that result. We drew those games and I was so unhappy.
"Someone is going to do it, and it'll be strange and you'll ask why, but tell me why not? If you have all the qualities in another goalkeeper to do something, or if something is happening and you want to change the momentum, then do it. It is a regret that I have and now my feeling is to get everybody engaged in the team that they have to play, regardless of the competition - this is my message.
"We adapt to the qualities that our players have and try to make them play to their strengths. There are games to do certain things and games to do other things that in my opinion were really important against Everton and we made the decision to try and benefit the team - that's it."
On what he expects from Ramsdale, he added: "The same as Jesus, the same as Tomiyasu - it is exactly the same. We play with 11 players, we don't play with 10+1 or 10 or nine, it is exactly the same."