Inductive Learning Hypothesis

With $n$ attributes, each with 3 values, we have that \[|H| = 3^n\]
We assume that one of those hypothesis will match the target function $c(x)$.
Furthermore, all we know about $c(x)$ is given by the examples we have seen. We must assume that the future examples will resemble past ones.
The inductive learning hypothesis states that any hypothesis found to approximate the target function well over a sufficiently large set of training examples will also approximate the target function well over other unobserved examples.
Why should this be true? Its not true for the stock market, or is it?