If an idea meets all four validation criteria, then you're free to move directly into product development if you choose! But you might instead choose to take a step back.
By working through the Lean Validation Process, you're sure to receive heaps of feedback from users. With this deeper understanding of the needs of your users you might realise that there's a bigger opportunity to tackle. In that case, you should feel free to pivot!
If you do, you can repeat the Lean Validation Process with your pivoted and improved product idea.
No matter which route you take, you can be confident that you're taking a strong idea into product development.