It means thinking in principles based on logic, with valid concepts and in full focus. In this context it means evaluating choices in accordance with a rational code of ethics applied to the values of your life. For the meaning of rational stands in a code of ethics see Ayn Rand's article on "The Objectivist Ethics". It isn't semantics. It isn't just predicting what will or will probably happen with a 'willingness' to accept consequences without regard to rational standards. You have to evaluate goals in a hierarchy of values and the means used to attain them, and engage in the mental effort necessary to think of what you need and possible means to get it, from the particular actions to the full principles of ethics to your own hierarchy of values.

From "The Objectivist Ethics":

"Rationality is man’s basic virtue, the source of all his other virtues. Man’s basic vice, the source of all his evils, is the act of unfocusing his mind, the suspension of his consciousness, which is not blindness, but the refusal to see, not ignorance, but the refusal to know. Irrationality is the rejection of man’s means of survival and, therefore, a commitment to a course of blind destruction; that which is anti-mind, is anti-life.

"The virtue of Rationality means the recognition and acceptance of reason as one’s only source of knowledge, one’s only judge of values and one’s only guide to action. It means one’s total commitment to a state of full, conscious awareness, to the maintenance of a full mental focus in all issues, in all choices, in all of one’s waking hours. It means a commitment to the fullest perception of reality within one’s power and to the constant, active expansion of one’s perception, i.e., of one’s knowledge. It means a commitment to the reality of one’s own existence, i.e., to the principle that all of one’s goals, values and actions take place in reality and, therefore, that one must never place any value or consideration whatsoever above one’s perception of reality. It means a commitment to the principle that all of one’s convictions, values, goals, desires and actions must be based on, derived from, chosen and validated by a process of thought—as precise and scrupulous a process of thought, directed by as ruthlessly strict an application of logic, as one’s fullest capacity permits. It means one’s acceptance of the responsibility of forming one’s own judgments and of living by the work of one’s own mind (which is the virtue of Independence). It means that one must never sacrifice one’s convictions to the opinions or wishes of others (which is the virtue of Integrity)—that one must never attempt to fake reality in any manner (which is the virtue of Honesty)—that one must never seek or grant the unearned and undeserved, neither in matter nor in spirit (which is the virtue of Justice). It means that one must never desire effects without causes, and that one must never enact a cause without assuming full responsibility for its effects—that one must never act like a zombie, i.e., without knowing one’s own purposes and motives—that one must never make any decisions, form any convictions or seek any values out of context, i.e., apart from or against the total, integrated sum of one’s knowledge—and, above all, that one must never seek to get away with contradictions. It means the rejection of any form of mysticism, i.e., any claim to some nonsensory, nonrational, nondefinable, supernatural source of knowledge. It means a commitment to reason, not in sporadic fits or on selected issues or in special emergencies, but as a permanent way of life."

Exactly the vituperation all too common here.

The question asks if EVERY decision must be based upon reason. The answer, as illustrated by my ice cream example, is no.

Okay, you win, you're right, I'm wrong, have a nice day.....