The more investment that happens before a thing achieves viability, the more likely it never achieves viability.

More investment typically takes more time.

Time to completing a real-world feedback loop is critical.

More investment means more time means longer loops to feedback means less likely to be viable when you finally interact with the ground truth of the real world.

But also every bit of investment you do before viability might lock in non-viable constraints.

When you invest incrementally in a thing post-viability, the incremental addition is more likely to be viable (you can quickly see if it's not and unwind).

But if the incremental investment comes before the thing is viable in the real-world, you can't tell if the incremental investment was viable or not… and by the time you do, it will have ossified and become load-bearing and will be more difficult to unwind.