From the book, Sartre for Beginners by Donald Palmer

A group of friends on vacation go for a day hike in the Alps. Half way to the mountain top, which is their goal, they turn a bend in the path and find their way blocked by a huge boulder that has fallen in such a a manner that it cannot be dislodged and cannot be circumvented. The first hiker’s stomach sinks in disappointment. “That’s it,” he says, ” The hike’s over!” …. From Sartre’s point of view, this person has chosen the facticity of the boulder as an insurmountable obstacle and chosen himself as defeated. A second hiker begins photographing the rock, excited by its sublime power and by the beauty of the landscape framing it. She has chosen the boulder as aesthetic object and chosen herself as a recorder of beauty – that is, as an artist. A third hiker examines the boulder scientifically, noting its mineral composition and the impact of its recent fall on the path. For her, this boulder is a motive for scientific study and is the occasion for her to act as a scientist. The fourth hiker says, “There is got to be a way around this thing,” and begins an series of experiments to overcome the obstacle. He has chosen the boulder’s facticity as a challenge and himself as hero.

The determinist argues that there must be something in the past of each of these hikers that determined their response. Sartre denies this. There is nothing in the facticity of the past of any of the hikers, nor in the facticity of the boulder, that necessitates any particular response to the boulder’s presence. For Sartre, the facticity of the rock is undeniable, but each person chooses the MEANING of that facticity for him or herself. Because facticity in itself is meaningless, the source of the meaning is a decision on the part of the individual. There are always alternative interpretations for meaning available; we are never confronted with only one possible choice.

There is always the most radical choice of all – the choice of death. A hiker might decide that the boulder’s presence is so depressing that he cannot go an living. This would of course be an ABSURD response to the boulder’s facticiy, but its mere possibility shows Sartre that all other responses were chosen as alternatives to death. If you did not kill yourself this morning (and apparently you didn’t) then you choose an alternative to death…. and you are responsible for that choice and for its consequences.