Frank was hammered by the home support for taking off the in-form midfielder during today's 2-2 draw with Manchester United.
The Dane said afterwards, "Yeah sometimes you are lucky but of course every single time I take a decision to sub a player it’s with one aim.
"To make the team win or get back into the game or try to see the game out. It’s with only one aim. To try to win the game. Mathys (Tel) did well, great goal, great involvement and in general I think Xavi did a fine game.
"A positive but also you need a bit of freshness."
Frank also said: "Of course, the emotions inside me are high but I take the positives out of this game. That’s what I believe and how I believe in building a good team and keep adding layers to it.
"Overall, a fine, good performance against a good Man Utd team which is definitely in flow."