Question

Why can't we walk on a frictionless surface.

Answer 1

To perform simple functions like walking or writing you need to make contact with a surface while moving one surface with respect to another which gives rise to friction.

In other words, friction occurs everytime when two surfaces come in contact. It is a contact force unless when you are using friction-less surfaces (which for now is a theoretical possibility). Thus friction occurs for every task that involes contact and relative motion of any two surfaces. The only walk that you can perform without friction is a space-walk while every other action that involves contact of two surfaces and motion involves friction. Therefore one can not walk without friction because there will be no contact force to make the person give motion.