The Lions boss has offered an insight into what motivated his side's push for promotion to the Championship.
Neil Harris believes Millwall's recent success is proof that pain is a powerful motivator.
As a player and manager, Harris has experienced both agony and ecstasy at Wembley Stadium but says defeat to Barnsley in the 2016 Play-Off Final was the driving factor when "times were tough" last season.
"The most influential thing was seeing Barnsley lift that trophy and celebrate with their fans a year earlier," Harris told millwallfc.co.uk
"That's why I had to watch Barnsley celebrate, as difficult as it was. It was the experience as a young manager, and my players as a young group, needed to move forward.
"We kept referring back to it over the past twelve months and my mindset was always to see my players lift that trophy."
The memory helped to spur the club onto a number of noteable feats including a giant-killing Emirates FA Cup run and securing promotion to the second tier of English football with a tense 1-0 win over Bradford City in the Play-Off Final.
"Our FA Cup run was a terrific achievement," he added.
"We beat Bournemouth, Watford and the Champions of England in Leicester - that's three Premier League teams. But that run was never our main goal.
"The Play-Off Final is what defines your season. We had 90 minutes to define our season and I believe if we hadn't beaten Bradford in the Final our season would have been a failure.
"That's why when the final whistle went I just felt relief for all of us.
"Then the celebrations started and to watch my players celebrate on the pitch was surreal. That is something they will remember forever."
You can watch the manager's season review on iFollow Millwall by clicking here.