It says, "The speed of light in vacuum (free space) is constant in all inertial frames of reference (i.e. for all observers)". To explain in a simple manner, "Light cannot be measured relative to any objects and is always constant in all inertial frames (which says Visible light is the maximum velocity allowed by nature). If something travels near the velocity of light, Time, Length and even Mass changes.

No... Of course there's no possibility for the second principle of Special relativity to be wrong. And hence for this reason, it was accepted and has been in existence for nearly a century.

It says, "The speed of light in vacuum is constant in all inertial frames of reference (i.e. for all inertial observers)". To explain in a simple manner, "Light cannot be measured relative to any objects and is always constant in all inertial frames. In other words, Light is the maximum velocity allowed by nature. If something approaches near $c$ - Time, Length and even Mass changes.

No... Of course there's no possibility for the second principle of Special relativity to be wrong. And for this reason, it was accepted and has been in existence for nearly a century. This restriction increased the interest for Physicists to concentrate on Tachyons