Player-manager Alex Neil admitted inexperience played its part as Hamilton Academical lost their Premiership opener 2-0 to Inverness.
Billy McKay and Ryan Christie profited from defensive errors in Accies' first top-flight game in three seasons.
"It was just an individual mistake and at this level you're going to get punished doing that," Neil told BBC Radio Scotland.
"It was disappointing but it'll be a learning curve for the young players."
The Lanarkshire side won promotion when they recovered from a 2-0 first-leg deficit to defeat Hibernian on penalties in the Premiership play-offs at the end of last season.
And Neil is confident they can recreate that battling performance to defy those who may expect them to last only one year in the top flight.
"I don't think it's fair enough to say we'll definitely be fighting relegation, however we're the smallest club in the league," he said.
"We've certainly got the youngest squad. We won't come away from what our philosophy is - to try and produce these young players and let them improve.
"It's up to us to deliver and try and prove people wrong."
And he added: "I think in the second half we certainly did a lot better. We did ourselves justice, we moved the ball really well, created some good chances.
"But, the first half - we've got to learn quickly at this level, to move the ball a little bit quicker.
"You're not going to get away with defensive mistakes, and that's what cost us the game. I think there was a wee bit of apprehension.
"Unfortunately Danny Mackinnon pulls out right before the warm-up.
"I'm still missing Jon Routledge and Tony Andreu as well, so in terms of having a full squad which was available at the end of last season we're missing a few, especially from the middle of the park, so I think that told on the game as well.
"We've got to learn, we've got to push on, we've got to improve."