After the Toffees ended a four-match winless run in the Premier League by beating West Ham 2-0 at home, they were brought back down to earth in their last outing as they crashed to a 5-0 loss at Stamford Bridge.
Koeman saw fault in "every aspect" of the team's display but believes his players shared the disappointment, and he is looking ahead to Saturday's Goodison Park contest against the second-bottom Swans in an optimistic mood.
The Dutchman, whose side are currently seventh, said of the November 5 game at Chelsea in which Everton were 3-0 down by half-time: "That was unacceptable.
"You can lose, but not in the way we lost, even against a Chelsea side as strong as they were that day
We made it too easy for them.
"I hate losing, but we can lose a game - we are not that quality that we will win always
But it's about the way how you lose a game, and that was not the way.
"It was a big step back that we showed, in every aspect of football - in intensity, in defending, in running, in quality on the ball.
"We need to improve, because that is not the team I like to see
But I'm really optimistic that we will get a very good reaction on Saturday
"It is always about the personality of the team, the players
We're playing at home and we're strong at home, and we have to show that again, and that what happened maybe can happen one day, but not more
"I have seen they understand the disappointment of what happened at Chelsea."
Everton defender Ashley Williams, who joined from Swansea over the summer, is set to come up against his former employers for the first time since the move.
Williams was with the Welsh club for eight years, skippering them for the latter part of that time, and Koeman admits the 32-year-old's knowledge of the opposition will be useful.
Regarding Williams facing his old side, Koeman said: "That is always special for players.
"He played a long time for Swansea and was really important - he was their captain, and of course, he has a lot of respect.
"He can give some good info about them
He is now an Everton player and I'm happy that we have him on Saturday in a blue shirt and not a white one."
Source : PA
Source: PA