Pochettino told the club's official website: "We played well for the first 45 minutes against Newcastle but we had a lack of concentration at the beginning of the second half and that changed the game. After that, it was difficult.
"It's important that the players realise the situation and what we need to improve. It's always good to be honest.
"Maybe it's a tough period but the only way to move forward is to work hard every day and believe and I believe in our skill, our way and our philosophy."
Pochettino's side face Aston Villa at Villa Park in their Premier League match on Sunday.