Brian Rice refused to blame Hamilton's disrupted week for their disjointed performance in Saturday's 2-1 defeat against 10-man Kilmarnock.
The Lanarkshire side were forced to miss training in midweek after three of their players went into self-isolation having initially tested positive for Covid-19.
Hamilton failed to capitalise on their man advantage after Eamonn Brophy was sent off for a late challenge on Scott McMann after just 23 minutes.
The visitors had recorded consecutive away wins before the trip to Rugby Park but they failed to register a single shot on target in the second half.
Rice refused to blame their interrupted preparation, though.
"I'm not using our build-up this week as an excuse," said Rice. "We were prepared for the game, we knew what we were doing so there are no excuses.
"I told them before the game that we had all the excuses in the world today if we wanted them but there is no excuse.
"The excuse is that we weren't good enough and I'm angry. I'm angry because that was the chance to get two wins in a row or at least four points from a possible six. We beat ourselves because we've done something stupid and that's my frustration.
"What happened during the week had no bearing on the result today. I told them at half-time that they could only beat themselves by doing something stupid and they did.
"We tried to play a crazy pass, it was intercepted and we were punished. We didn't show enough urgency or enough quality to get back in the game."
Nicke Kabamba capped a lively performance with the winning goal in the 57th minute after Ryan Fulton parried Gary Dicker's strike into the path of the striker.
Earlier, Hakeem Odoffin had equalised for the visitors from close range after Greg Kiltie's excellent low strike gave Kilmarnock the lead.
The 23-year-old has struggled with injuries over the last few years but his impressive start to the season drew praise from his manager Alex Dyer.
Dyer said: "He's earned the right to be seen as an important figure.
"He had a bad injury which kept him out for nearly two years and sometimes it takes a while to get back fit.
"He worked hard in pre-season, got the opportunity to play and he's proving his worth.
"He looks really sharp and hopefully that'll continue because it's going to be hard for me to leave him out."
