text: Pai Mei invokes this trope in Kill Bill Vol. 2 while training The Bride; "Since your arm now belongs to me, I want it strong."
  We see a form of this in Harry Potter and the Goblet of Fire where "Mad-Eye Moody" nudges and helps Harry along in his Tri-Wizard Tournament challenges, for the sole purpose of luring him into a death trap If he isn't good enough to reach the Triwizard Cup, then he won't reach the cup.
  In The Pendragon Adventure, this trope is the reason Saint Dane doesn't simply kill all the Travelers. In fact, it's also the reason he even lets Bobby find him in any territory at all. When Saint Dane says he's done with his work in a territory, he means it.
  In Artemis Fowl: The Opal Deception, Opal waits a year before having herself revived from her self-induced coma. This is partly because she wanted to throw off suspicion. It's also, though, because she wanted to wait until Artemis, Butler, Holly, Commander Root and Foaly were all back at the top of their game before unleashing her new plan so that victory would be that much sweeter.
  In Knight Life, after Morgan Le Fey's (Morgana's) latest plan to destroy the mayoral ambitions of Arthur Penn (Pendragon) fails, she decides that if he thinks things are going great now, then it couldn't help to build up his hopes even further. She'll make it seem like things are going well with the election, only to crush his dreams at the last minute.
  Morgan: All right, fine. You want to build up your hopes, Arthur? Fine. I'll build them up even higher, then, and that way they'll make an even louder crash when they fall! And nothing will distract me from my purpose! Nothing!
  In the updated Battlestar Galactica, it's never exactly clear why the Cylons didn't simply Zerg Rush the fleet, destroying Galactica and picking off the rest of the fleet at leisure. After all, they'd wiped out 99% of humanity already. Why tiptoe around killing the rest? The show never says outright, but heavily implies, that this was Cavil/One's doing: He wanted to prove to the Final Five that Humans Are Bastards and not worth saving (thus justifying his own hatred of the Five and humans) by hounding what was left of the Colonies until they turned on each other (which sort of was the case). The hypocrisy of this did not go unremarked upon.
  In Mahou Sentai Magiranger/Power Rangers Mystic Force, Wolzard/Koragg wants the heroes (mostly the red ranger) to be as strong as possible so they'd be Worthy Opponents. There's more to this than just him being an honorable Blood Knight though. He's actually the red ranger's father (the whole team's father in the Sentai version) who has been brainwashed by the Big Bad, but still maintains some of his old self.
  In Kaizoku Sentai Gokaiger episode 28, the Monster of the Week is an alien bounty hunter and thrill-seeker who does it twice. In the past, he nearly killed Captain Marvelous but stopped short and even injured himself to create a weak point and taunted Marvelous to come back strong enough to challenge him. Then in the present, he handily defeats Marvelous a second time (mostly due to his being paralyzed by fear) and leaves mid-fight despite being paid to kill the Gokaigers.
  In the Supernatural episode "All Hell Breaks Loose, Part One" (S02, Ep21), the Yellow-Eyed Demon reveals that he has been working to make Sam stronger as part of his Evil Plan.
  Reverse-Flash wants Flash to master his speed powers, so that he can force Flash to travel through time and return him to his home in the future.
  Likewise with Zoom, who spends the first part of the second season sending out supervillains for the Flash to practice on, though in his case he wants to kill Barry and take his speed.
  In Dragon Ball Fighter Z, Big Bad Android 21 has the power to turn people in sweets, but she wants the fighters she faces to be as strong as possible, since stronger fighters taste better to her. Too bad for 21 that Goku and company get stronger than she can handle, and she's wiped out in all three story arcs by her own gluttony getting the better of her.
  In Final Fantasy IV, Golbez can't get into the Sealed Cave himself. Cecil can, but isn't strong enough to get through the deathtraps on his own. Cue the Sorting Algorithm of Evil.
  And in Final Fantasy XIII, this is indicated to have been in effect for the first portion of the game. Someone rather high up wants the Pulse l'Cie to get stronger. Turns out it's Primarch Dysley, a.k.a. the fal'Cie Barthandelus, as part of his Thanatos Gambit. He can't kill himself or even go easy on the Pulse I'Cie so they have to be strong enough to sincerely kill him.
  Happens again in Final Fantasy XV. The main villain Chancellor Ardyn Izunia arranges the supposed political marriage between Noctis and Lunafreya which conveniently sends him on a roadtrip away from the false peace treaty (which the villain also arranged) between Niflheim and Lucis. So while Lucis falls, Noctis is safe. The villain later briefly joins the heroes on their trip without revealing himself to help get them started on the quest to unlock Noctis' full power. In the end, as Noctis is absorbed by the Crystal, Ardyn reveals his motives. Turns out he's an immortal member of Noctis' bloodline who wants revenge on the Astrals and their "chosen" for being rejected after he had tainted himself absorbing countless daemons in his quest to heal people of the Starscourge. While he could have killed Noctis at any time, doing so would have brought him no satisfaction. Ardyn wants Noctis to become the "King of Light" because that will make killing him even sweeter.
  Turns out, this is the real reason why Bahamut chose Somnus, Noctis' ancestor, to be the Founder King of Lucis. Ardyn, absorbing so many daemons that he became the immortal physical embodiment of the Starscourge, can no longer be rid off even by the Astrals. So the Astrals chose their second best option in order to propagate a bloodline that keeps adding strength and wisdom stored inside the Ring of Lucii in hope to be strong enough to finally kill Ardyn. When Ardyn attempted to kill Regis, Noctis' father, before he was born, Bahamut stopped Ardyn under this reason; the Caelum dynasty almost completes its purpose and Ardyn should spare the bloodline for one more generation to finally be destroyed. Ardyn, one way or another, agreed to this because he really wants to die.