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C'est parfait! Trying to measure the spin of an electron is quite similar to tossing a coin. The way you get only Heads and Tails on the coin, you can only get $$+ \frac{1}{2}$$ or $$- \frac{1}{2}$$ for an electron's spin.
More importantly, just like you don't know what the result of the toss is, you won't know if you will measure the electron's spin to be $$+ \frac{1}{2}$$ or $$- \frac{1}{2}$$.