To shift the function \( f(x) = (x + 1)^3 \) to the left by 3 units, you need to replace \( x \) with \( x + 3 \) in the function.
The new equation will be:
\[ f(x) = (x + 3 + 1)^3 = (x + 4)^3 \]
Thus, the function shifted 3 units to the left is:
\[ f(x) = (x + 4)^3 \]