This is a must-read for potential PhD students. The essential tag-lines are listed below, but be sure to read the full article.

Misconception 1: Anyone who starts a graduate degree and does not finish it lives the rest of his or her life permanently embittered, resentful, and with a sense of personal inferiority.
Misconception 2: All academics are smart people, and all smart people are academics.
Misconception 3: Everyone who deserves a Ph.D gets one.
Axiom 1: There are plenty of jackasses with Ph.D's, and plenty of brilliant people without them.
Axiom 2: Most people without graduate degrees live perfectly contented, fulfilling, and successful lives.
Axiom 3: Graduate school is not fair. It does not necessarily reward intelligence, preparation, perseverance, and ambition with the hoped-for degree.
Corollary 2.1: A Ph.D doesn't necessarily make its holder happy.
Tip 1: Before you sign your first graduate school application, decide how much you are willing to give up for your Ph.D.
Tip 2: Always have an escape route from graduate school planned.

Link (Webpage Dorothea Salo)