His players reaction to allowing Arsenal to nick a point on Sunday also told Pochettino they are finally getting there.
“It’s a good thing to be disappointed,” he added. “Arsenal were in a different level a few years ago and a draw in a big derby was a good result.
“But now when you only draw with Arsenal, to feel disappointed is a good thing.
“We have changed our mentality. It was a game we should have won.
“But we show we can compete in this level against Arsenal a team who have always been in the Champions League over the years few years and invest more money than us. Belief is the most important thing.”
A solid defence will come in handy tonight as well with Dortmund having scored 61 times in just 19 home games this season.