Truro City manager Steve Tully admitted his side "couldn't solve Hemel Hempstead's puzzle" as they were beaten 2-1 away at the Hertfordshire club.
Shane White equalised, but City suffered only their second National League South defeat since August.
"Sometimes you need that reality check and we definitely got that," Tully told BBC Radio Cornwall.
"We had players that are normally eight or nine out of 10, but they were five or six and you can't carry that many."
The Cornish side remain in the final play-off place and have played fewer games than all of their promotion rivals.
Tully warned before the match that his side's 10-game unbeaten run would soon come to an end.
"We had a puzzle to solve and we didn't solve it, that's probably the best way to describe it," he added.
"The players will be hurting, like myself and Wayne (assistant boss Wayne Carlisle), we don't like losing games but we'll dust ourselves off and be ready to go again on Tuesday."