In most video games, especially of the 8-bit era, the controlled protagonist character either dies or takes injury upon contact with a harmful object or enemy. In classic titles such as Super Mario Bros. or Mega Man, the moment an opposing pixel touches the pixel boundary of the on-screen Mario or Mega Man character, damage is taken.
Largely, this is the norm. For certain titles, such as some shoot-'em-up games, the "hit box" for an animated sprite may actually be a smaller target within the on-screen drawn protagonist. In other words, errant projectiles can actually slide through the outer boundaries of the visible character without taking damage. This can enhance tactical emphasis, hone reaction times and hand-eye coordination even tighter, and generally make for a more complex skill level depth potential.
Furthermore, in some games, especially fighting games, there is a "block" function that, even if an opposing character makes contact with yours, reduced damage is taken, or even none altogether.
Then... there's Karate Champ. Now, Karate Champ on the NES does have a block function -- but watch the video, especially at the 45-second mark. Can you honestly tell me that every time pixels cross, a character is blocking? No, you can't. This game is complete and utter chaos, with the characters even teleporting position completely at one point. Ridiculous.