Millwall manager Neil Harris says he and his team will take lessons from the Sky Bet League One play-off final defeat to Barnsley.
The Lions were beaten 3-1 at Wembley on Sunday, and they fell behind inside two minutes as Ashley Fletcher struck before a wonder-goal from Adam Hammill doubled the lead.
Childhood Barnsley fan Mark Beevers pulled a goal back before the break, but Millwall were dealt a hammer blow when Lloyd Isgrove headed home the Tykes' third to seal their return to the Championship.
But Lions boss Neil Harris - who has tasted play-off defeat with the club as a player - was determined that his side would learn from the experience.
"I've just said that I'm proud of them. What we've achieved was unexpected at the start of the season," the manager told Sky Sports.
"There's huge disappointment, of course there is with me for but my players and staff in there, we're gutted. We've come so far as a group and we just couldn't finish it off today.
"There's no excuses, we're not making excuses because we still have quality players in the squad. I think the key is that we learn from this, I've learnt from it myself and we come back better and stronger next year."
Millwall were forced to change their starting line-up just minutes before kick off as Byron Webster pulled up during the warm-up, and Harris believes it did have an affect on their performance.
"It affected us mentally before the game and we tried to paper over it with the club captain Tony Craig coming in to lead the troops but we worked all week on our game plan and set plays and it all sort of goes out the window in the warm up. It's definitely a learning curve for me and certainly for my players.
"The goal did give us hope but we never really built the momentum after that. Even if we got to 2-1 going into the last 15 minutes and we could bring the attacking players on, I really fancied us to get the chance.
"I think it was clear that the chances we made, we didn't put them into the net and that was the difference today."
The south London club will now begin next season in League One, but the manager is already targeting another promotion push back to the second tier.
"Obviously it takes some time to digest and get over today. We go away for the summer now but my message to my players is that we come back better next year and we come back to gain promotion next year.
"This year was a great year for us to learn and next year we have got to be better."