In his quest to get closer to Death, Thanos once sacrificed himself in a moment that turned out to be his biggest failure and a colossal mistake. In The Thanos Imperative, the Mad Titan surrendered to Lord Mar-Vell and told the villain to kill him. However, his sacrifice backfired tremendously as Death didn't see his actions as worthy of her attention and affection - leading Thanos to become incredibly angered after being spurned by his greatest love once again.
Thanos's affection for Death has led the villain to rewrite reality and kill countless Marvel heroes. But, perhaps, the Mad Titan's greatest attempt at winning Death's hand was during The Thanos Imperative storyline. In the arc, Thanos is resurrected and immediately comes into conflict with Lord Mar-Vell, an evil version of Captain Marvel who rules the Cancerverse. After killing Drax the Destroyer, Mar-Vell confronts Thanos, who shockingly bows down to the alternate version of the cosmic Avenger. Thanos tells Lord Mar-Vell he should kill him so that Death may die for good - which turns out to be a huge trick.
In The Thanos Imperative by Dan Abnett, Andy Lanning, Miguel Sepulveda, Jay David Ramos, and VC's Joe Caramagna, Thanos submits to Lord Mar-Vell. After summoning monsters that constrict Thanos, Mar-Vell impales the Mad Titan with a sword. As Thanos dies, he reveals that he tricked Lord Mar-Vell, as Death arrives and kills the villain for cheating death twice. Thanos thinks he's won and asks for Death's hand after killing an entire universe (the Cancerverse) for her. However, Death has no interest in being with Thanos as she rejects his pleas and walks away from him without saying a word. Thanos fails as he mistakingly believes his action would win Death's affection. That proves to be a mistake in judgment.
Ultimately, his failure to win Death's love again causes Thanos to lose control. Unfortunately, his sacrifice proved pointless in his goal to win her hand. After directing his anger towards the Guardians of the Galaxy, Star-Lord and Nova use the Cosmic Cube to trap Thanos (and themselves) in the Cancerverse. In the end, his mistake led to his imprisonment.
The Thanos Imperative proves to be quite an embarrassing story for Thanos, as his mistakenly placed blind love for Death causes him to sacrifice himself - and once again, the Mad Titan is forced to watch her not even give him the time of day. Thanos loves Death more than anything, but in this case, his biggest sacrifice turned out to be his most significant self-own and failure.