1. **State the problem:** Simplify the expression $\frac{1}{2} - 1$. 2. **Recall the rule:** To subtract a whole number from a fraction, convert the whole number to a fraction with the same denominator. 3. Convert $1$ to $\frac{2}{2}$ because the denominator of $\frac{1}{2}$ is $2$. 4. Rewrite the expression: $$\frac{1}{2} - \frac{2}{2}$$ 5. Subtract the numerators while keeping the denominator the same: $$\frac{1 - 2}{2}$$ 6. Simplify the numerator: $$\frac{-1}{2}$$ 7. **Final answer:** $$-\frac{1}{2}$$