The Bruins interpret their No. 4 seed as a disappointment, a measure of points frittered away, especially in the second half. Meanwhile, the Maple Leafs are thrilled to be here at No. 5, their first postseason berth since 2004. Now we see how those two very different psychic energies play out in the first postseason meeting between these two since 1974. It’s the only Original Six matchup in Round One, and somewhat unexpected. Until the Bruins went 0-1-1 over the weekend, it looked like Montreal and Toronto would do the Original Six honors. The bond here, of course, is Phil Kessel, the ex-Bruin forward who forced the trade that ultimately brought Tyler Seguin and Dougie Hamilton to Boston. The Garden crowd again will be belting out, “Thank you, Kessel!’’ hoping he continues to post goose eggs vs. his old homeboys. But there is much more to this Blue-and-White group nowadays. The attack is deeper and coach Randy Carlyle, who won a Cup in Anaheim, is far more astute at matching up combinations. The Bruins need to be less concerned with Kessel than how to shake their own late-season lethargy.