Austin MacPhee admitted Hearts were lacking confidence and firepower after he signed off on his interim manager role with a 1-0 defeat at Motherwell.
Christopher Long's 40th-minute goal lifted Motherwell into third place in the Ladbrokes Premiership and left Hearts level on 12 points with bottom two Hamilton and St Johnstone.
MacPhee's six-match caretaker role came to an end after Hearts confirmed Daniel Stendel as their new manager on a two-and-a-half year deal.
The visitors took nearly an hour to get a shot on target, when Ryotaro Meshino's effort was comfortably held.
Hearts are without strikers Conor Washington and Steven Naismith with hamstring injuries – the latter facing about two more weeks out – and MacPhee admitted they did not have enough belief in front of goal.
"They have scored from their first shot on goal and it rocks us.," MacPhee said. "You can see the confidence isn't in the team. There is maybe a wee bit of a lack of belief that we are going to score without Washington and Naismith, especially away from home.
"We came back into the game and maybe looked a wee bit more of a threat when we went to 3-5-2 from 3-4-3 when Uche (Ikpeazu) came on but we lacked cutting edge at the top end of the pitch."
Motherwell survived a bug outbreak to record a third consecutive win and clean sheet.
The illness saw Peter Hartley and Devante Cole start on the bench and deprived them of Christy Manzinga but they got on top in a tight first half before Jermaine Hylton nutmegged Craig Halkett to set up Long to sweep into the roof of the net.
Manager Stephen Robinson said: "Jermaine Hylton I thought was class all day. He gets to the byline, before he might have slammed that across goal. We have worked on him cutting balls back.
"And it's a great finish from Longy. I think there's more to come from him. He's got raw ability, you see his pace, he caused them massive problems. He was excellent throughout the game, was a constant thorn.
"If Longy believes he is as good as I think he is, then he has an excellent chance."
Motherwell had a second goal disallowed for offside when Allan Campbell helped on Liam Polworth's shot from close range.
"From what I'm being told it was a goal, it was onside, and I believe that would have finished the game off," Robinson said.
"When it's only 1-0, you are under a bit of pressure still. They launched every ball into our box but I thought it was a really mature performance.
"We stood up to that physical element and I thought we thoroughly deserved to win."