One example: Once I imprisoned the Purple Man, a villain capable of making anybody do anything he ordered, and used his powers to conquer the world. When the Purple Man told Doom he did not deserve to rule because he did not possess any powers, Doom ordered all his servants to leave the room, took down all the barriers holding the Purple Man, removed his mask, and dared him to lend credence to this charge. Note that the Purple Man was in a power amplifier that was boosting his abilities to planetary scale at the time.
Doom: I am removing my mask, Killgrave. Within it is the circuitry that shields me from your power. I am totally vulnerable.
Purple Man: Then release me. (Doom doesn't move) I-I said release me! (Again, Doom doesn't move.) Stand on your head! T-take a flying leap! KILL YOURSELF! (Doom doesn't do any of those.) I-impossible! Not this close! No one has a will that strong! No one...
Doom: Now, Zebediah Killgrave...who deserves to rule?
As shown in the main page, the fact that in one dimension I was the only one in the entire universe to resist being consumed by a zombie plague through sheer willpower alone is a perfect example of the iron determination possessed by Doom.
Another one would be saving Susan Storm, her daughter, and Johnny Storm when Richards couldn't do anything to help them. And then ensuring he would never forget his debt to me by naming the newborn child after my former beloved, Valeria. He should be pleased Doom condescended to give such an honor to an infant. Whom no one will ever harm. Doom guarantees it.
Norman Osborn once thought it wise to sic his omnipotent lapdog the Sentry on Doom. I obviously anticipated this and sent in my stead a Doombot armed with cybernetic locusts that swarmed his pitiful Avengers Tower. Osborn threatened me with retaliation but Doom had foreseen his lack of resolve and called his bluff. Soon after, his own government arrested him. Doom still stood unopposed.
Doom rescued the soul of his mother from Hell. It required the minor assistance of the Aged Genghis and Doctor Strange — but did I ask any of them for help? No! Doom will be in debt to no one. If I offered the slightest tokens of respect to either of them, in the end I was still captain of my own soul. Do not pity Doom! Regardless of what it may have appeared to cost me, I achieved exactly what I wanted.
Of course, there was the time I fought Red Skull on the moon and let Steve Rogers remember that as a Romani, Doom earned his chance to make that Nazi swine pay.
When Doom was in the time of King Arthur with Iron Man, no mere parlor tricks like Stark used were needed to impress Arthur; the Seal of Latveria I wear as its rightful sovereign was enough for the proper respect.
When Reed Richards was out of action and the Fantastic Four (or what remained of them) were facing off against an impressive psychic power called.. No, that would be telling. Let the following quote show you why exactly the Fantastic Four came to Doom for aid.
"Turn your eyes from the Torch, Over-Mind — DOOM approaches!"