Quique Sanchez Flores felt Watford "looked a bit soft" after suffering a 4-0 defeat at the hands of Arsenal on Saturday.
The tone was set when Arsenal - needing a win to remain in the hunt for the Premier League title - opened the scoring through Alexis Sanchez inside the first five minutes at Emirates Stadium.
Alex Iwobi doubled the home side's lead before the break, with a deflected effort from Hector Bellerin and a close-range finish from substitute Theo Walcott completing the scoring.
"It is the first time we have conceded four goals this season - we are not happy with that," Flores told Sky Sports.
"Once we conceded the first goal inside the opening minutes, it was quite difficult for us. Arsenal played really well - they played really fast, really quick. It was difficult to stop them.
"But we need to learn, because the players and staff are not happy with that performance.
"We looked a bit light, a bit soft. This is not our style."
Watford have now won only two of their last 14 league games, a worrying slump in form that has seen them drop down to 14th in the table.
While they are still 10 points clear of Sunderland, who occupy the final relegation spot, Flores has warned the club not to take their top-flight status for granted.
"At the moment we have 37 points. It's a very dangerous time, because it is possible for us to get confused over whether we are safe or not," he said.
"We need to finish the season in the best way possible. The players deserve to finish in an amazing way because they have worked so hard throughout the season."
The Spanish coach also revealed the early substitutions of Etienne Capoue - who was replaced during the first half - and Odion Ighalo, who did not return to the field after the break, were made for tactical reasons.
"When I'm not happy with the performance of one player, or when I think have to change tactically or technically, for me it is not about the minute."