Taking the software example, you can easily scale from 1 to 100 users on your own machine. You can handle thousands by moving to a shared host. Using off-the-shelf web servers and load balancers will help you serve a million+. From there on you'll have to spend a lot more effort optimizing and fixing bottlenecks to get to tens, maybe hundreds of millions. What if you want to handle a billion users? Five billion? Ten billion? It always gets harder, not easier.
Pushing the established limits of a problem takes exponentially more effort than reusing existing solutions, even though the marginal improvement may be a lot smaller. Getting from 99.9% to 99.99% efficiency takes more effort than getting from 90% to 99%, which takes more effort than getting from 50% to 90%.
You never pierce the scaling wall. It only keeps getting higher.