Why couldn't anything travel at 100% the speed of light?

Cherenkov radiation happens when electrically charged particles, for example, protons or electrons, travel quicker than light in a reasonable medium like water. At the point when this occurs, the water particles and particles connect to emit light.

How can it be to travel quicker than the speed of light?

Light slows down to 75 percent of its normal speed when it travels through water. This allows the particles emitted from nuclear fuel to move faster than light in water.As these charged particles disrupt water molecules in their path, light particles, known as photons, are released — creating a visible “shockwave” of blue or violet light.

from

https://www.energy.gov/ne/articles/cherenkov-radiation-explained#:~:text=Cherenkov%20radiation%20happens%20when%20electrically,a%20clear%20medium%20like%20water.