לזכות שמחה בן נעכא גיטל שיהיה כאחד הגדולים אשר בארץ
R. Huna said: If one is travelling on a road or in the wilderness and doesn't know when it is Shabbos he must count six days and observe one..
Raba said: Every day he does sufficient for his requirements [only].
Asks the gemara - And on that day he is to die?
The gemara answers that on Friday he prepares for two days of work.
This gemara is a wonder. The gemara asks how we can forbid a person from preparing food for one lest he die. If a person refrains from eating for one day he will die? If so, today on Asara Biteves we are all in big trouble...
Many answer that since the person is eating very skimpily for six, fasting on the seventh will in fact be a danger for him.
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We see from this gemara that despite the fact that when he prepares a double portion on Friday he will be possibly desecrating Shabbos [because right now he doesn't need the second portion] not for the sake of pikuach nefesh [if it turns out that it is really Shabbos that day] while if he prepares one portion all seven days he will desecrate Shabbos for the sake pikuach nefesh, we nevertheless tell him to do the latter. It emerges from this gemara that we prefer that he avoid definitely desecrating Shabbos [even for pikuach nefesh] and instead risk possibly desecrating Shabbos not for pikuach nefesh. This is because we always prefer that he transgress a ספק איסור and not a ודאי איסור. [See אהליך יעקב עמ' קפח מש"כ בזה]
There is a lot more to learn from this gemara and maybe for another time.
