The Cottagers fell to a heavy 4-0 defeat to Liverpool at Anfield to lose their seventh game of the season.
Jol told BBC Sport: "We've had a difficult schedule and the task here became too big after conceding two early goals. We do everything in training and then we make the same mistakes.
"It was very frustrating, not only for the fans but for me and the team. But I can't come up with the same excuses, that we played better in the second half, because in the end we did not get a result.
"If you concede goals here, you have to open up a bit, but in the second half we tried to keep the damage down and that was the strategy. It was not enough for me and not enough for the team. I've got ambition and a mentality to win."
Fulham are currently 16th in the Premier League.