Why are the concepts of random selection and random assignment important?

Question

Quizplus · Accepted Answer

The Answer is Random selection ensures that every member of the population has an equal chance of being a participant in order to make the study generalizable to the population being studied. Random assignment gives each participant an equal chance of being assigned to each condition so that the groups within each condition are comparable to the others, except in terms of the independent variable.

Why Are the Concepts of Random Selection and Random Assignment