I'm no sports psychologist, but have read many books to help in my own performance (music).
In technique, a 'meaningful' face-off is no different than any other. But in practice, it's an entirely different mindset.
With nobody watching, many could kick a 42 yard field goal, including high schoolers. But with a Superbowl or playoff game on the line, it's very different. Just ask the Buffalo Bills.
My read on the Bruins over the past several years is this: they've mastered the Inner Game (mental) by being even-keeled. They don't let themselves get too high after a win, or too low after a loss.
More importantly, this has made the players successful in life in general. I recall an interview with Tuuka Rask at the start of the 2019-20 season, just months after the devastating Game 7 Cup loss. He was sporting a tan, jovial, and happy; whereas many fans still hadn't gotten past the loss.
While this mentally balanced approach has helped them, I feel it has also hindered. They lost 3 home games including a Game 7 in 2019, with some mental lapses inexplicable for what was at stake. They had a 3-1 lead against Florida, including a one goal lead with a minute left in Game 7. They not only couldn't win a face-off, they couldn't get a simple clear; which has repeated this season.
I don't view them as choke artists; rather, I see them not elevating their intensity in key situations and games, when their opponents do. Just look at Matthew Tkachuk through the entire playoffs. If the B's could get that fire in their bellies, they'd be even scarier. They had that in 2011, from Tim Thomas on out.
The reality is, their lives don't depend on the outcome of a face-off, a game, or a series. But their opponents often play as if their lives did.
I'm all for practicing face-offs; but I think some mental adjustments are equally important.