Boss Di Matteo calls for the Baggies to not lose their focus
The Baggies have had four consecutive defeats in the league and have only picked up seven points from 11 games.
That is in stark contrast to their early season form, which saw Arsenal beaten at the Emirates and Manchester United held 2-2 at Old Trafford.
But Scharner believes his side have to have a good mental attitude if they are to come out of the this slump.
He said at a press conference: "The mental side of the game is even more important now than it has ever been.
"You have to be able to cope with all of the pressure because every small detail on the field matters.
"Everyone in the Premier League is fit enough to compete. They are strong and, most times, they are technically good.
"But there is another dimension. There is another five to 15 percent that comes from your belief and that can be the difference over the other team."
West Brom travel to London tomorrow with a growing injury list, with manager Roberto Di Matteo without Steven Reid and Pablo Ibanez following the weekend game and Gabriel Tamas is still suspended.
But Scharner wants the Baggies to take heart from their early season away performances.
“The results we have had away from home in particular this season have been very pleasing," he said.
"To win at Arsenal and Everton for the first time in 30 years or more, and to get a point at Manchester United after being two goals down were great results.
"It shows the quality we have here, and how high the potential is in the squad."
The tight nature of the league table this season has seen teams tumble down and jump back up the table, but manager Di Matteo insisted that he was only concentrating on his own side's performances.
"We have to look at what we do ourselves," said Di Matteo. "We can't influence other teams."
He continued: "People expected us to be at the bottom and we've never really been there. Now we have to take the positives out of that and try to do it in the second half of the season.
"We have done well to be where we are at this stage of the season.
"There has been a great opportunity to add points over the last few games, which we have not done.
"But we had already had points, which I said would be important for when we weren't getting any."