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 \(- \frac{1}{2}\).