"Hitchcock has a term that he labeled 'TheMcGuffin.' For him it was just the thing that the main character either wants to avoid or obtain, and to him it was unimportant what the McGuffin? was so long as the person wanted it bad enough. It’s kind of the same way… I feel all of our magical charms and stuff, they’re all McGuffins?. You know, they need to have a cool name, they need to have good fight scene, but it’s just a spell. (laughs) It’s just a way to keep going with the story." - JamesMarsters
TheMcGuffin is a plot device utilizing an element which may or may not be integral to the overall climactic conclusion of the story, but moves the plot forward nonetheless, and keeps the audience's attention.. It is generally something that concerns one or more major characters. In it's most ideal form, TheMcGuffin is what the entire plot revolves around, yet has no real significance.
One can see TheMcGuffin throughout Hitchcock's works, but it's also prevalent in Whedon's work. For BtvsSeasonFive, {{Glory}}'s McGuffin? was TheKey?, which we knew was DawnSummers but she didn't figure that out until near the end. It boiled down to a process of elimination for Glory. Is {{Spike}} the key? No. Is Tara the key? No. Is Buffy? And on and on until she got to Dawn. Like playing Battleship. Strategically it's what drove the plot of the season's arc. For part of Btvsseason four, Buffy's McGuffin? became Room 314. What lay behind that door? What was Walsh trying to hide? The primary difference between Whedon & Hitchcock however when it comes to McGuffins?, is that Whedon usually eventually resolves the McGuffin?. It's not just a means to an end. It is the destination of the journey. For Hitch it wasn't relevant to the story, and he often used it as a red herring, to throw the audience off the trail. For Whedon, it's the character's short duration Holy Grail. Or it's an answer that leads to another question. A step in the journey that provides the protagonist with a new direction to go.
In AtSSeasonTwo, From the episode FirstImpressions all the way to {{Reprise}}, {{Angel}}'s Holy Grail was {{Darla}}'s redemption. Angel turned his back on everything that mattered to him, believing only he alone could win Darla's redemption. He succeeded in TheTrial, but due to a loophole (Darla'd already been given a second chance and was undeserving of a third) all Angel's efforts were wasted. Even then though, he didn't want to admit defeat. Up to the point where Drusilla turned her again. So then the McGuffin? became the SeniorPartners themselves. He wanted to take them down. One by one if necessary, until Manners showed him the futility of that goal. Angel succeeded in taking down one, even got a ring that'd lead him to the others. Manners convinced him that the "home office" was the same reality he'd been fighting for. Angel believed this meant nothing he did mattered. He truly became lost. Then The Host showed him that this journey had caused him to lose his focus. Doyle had cautioned Angel in season one that without human interaction he'd lose his place in the world, and Angel had done just that. He'd come full circle. He was nothing without his friends.
So it's not the achievement of a goal that matters. It's the journey. It's who you have with you along the way. However, if the character doesn't invest all of himself in the goal, regardless of the futility, we get bored. One could argue that this is why Buffy Six or the latter part of Angel Two is weaker than other parts of the two series - because the protagonists in question had lost that intensity.
Weird how that works.