Quoting: HabsForEver
It's a great feeling for sure, but it's still not a successful season if they lose. It's a great feeling because of how close we are to being there.
That's a sad outlook on life. Statistically speaking, if you win a cup once in 31, soon to be 32 (Seattle) years your doing fine.
If you think winning the Stanley Cup is the only definition of a successful season than you're going to be disappointed with your team for most of your life.
Going to the ECF and knocking off the 1 and 2 seeds was a successful season. Going to the ECF final in 2014 and beating the Bruins in a game 7 was a successful season. Heck, even getting 96 pts in 2018-19 was considered a success.
Everyone wants to see their team win the Stanley Cup. You don't just go from lottery pick to Stanley Cup, it takes time. Each minor success builds towards the ultimate goal of winning the Cup.