A black hole is a mass concentrated into an infinitely tiny point. This causes immense and strange gravity, which gets more and more intense as one gets closer to the center. If someone traveled inside a black hole, they would experience a tidal force, or a difference in gravity, between their head and feet. Because the gravity is increasing so rapidly as you draw near the center of a black hole, your head (assuming you descended feet first) would experience much less gravity than your feet. These tidal forces would not bode well for us humans, or any object traveling into a black hole. When the head and feet are pulled upon differently by the black hole's gravity, a one would be stretched out in a process known by scientists as spaghettification. It would stretch you out, breaking your body in half and eventually reducing you (or any object entering a black hole) into a thin rope of atoms.
This isn't the case for all black holes. For relatively small black holes closer to the mass of our sun, spaghettification would take place. However, in larger black holes the gravity increase is spread out over more distance. Therefore, the tidal force is not as large and spaghettification would not take place.
[P1] In black holes, the gravity increases very quickly. [P2] If one descended into a black hole, the gravity would be larger on their first point of entry. [P3] The difference in gravity would stretch them out, resulting in spaghettification.
Rejecting the premises
[Rejecting P1] Large black holes don't increase quickly enough to be significant.