Innovation is finding new solutions to pre-existing problems given new constraints.
Pull the sentence apart and it has three moving parts.
Pre-existing problems. The problem was already there. Innovation rarely invents a new need — it answers an old one that was waiting for a better answer. What we call novelty is usually a fresh response to a familiar question.
New constraints. Something changed: a technology, a cost, a law, a material, an expectation. The constraint is the variable. When it shifts, the space of possible solutions shifts with it — some doors close, but others open for the first time.
New solutions. The new answer isn't willed into being by cleverness alone. It becomes both possible and necessary because the constraint moved. Possible, because the new constraint permits what the old one forbade. Necessary, because the old solution no longer fits the new terms.
So innovation is less about the problem changing and more about the constraint changing. Find the constraint that moved — or move it yourself — and the new solution is what falls out on the other side.