Top duelists are dumb

[withheldforprivacy]

-Kaiba giving up the idea of fighting Pegasus with duel discs, just because Mokuba would wield Pegasuses
disc. Kaiba knew his only hope of defeating Pegasus was with those discs. So, if he really cared about his
brother, he should go with the initial plan. It's not like Mokuba would get hurt from a duel.

-Yugi wanting to fight Joey at Battle City semi finals. That way, he would allow Marik to get a second god card.

 

[Pyro]

Using the duel discs wouldn't have increased Kaiba's chances at all, not against Pegasus' hax.

 

[withheldforprivacy]

This isn't explained well in the anime. But, in the manga, at Duelist Kingdom saga, the duels took place on
tables with holograms. Kaiba explained that Pegasus probably has to be close to the foe to read his mind, so,
with the distance the use of duel discs would create, Kaiba hoped Pegasus wouldn't be able to cheat.

 

[Pyro]

That makes sense. I haven't read that arc of the manga.