Software fragility is actually very similar to physical fragility.

Think of Jenga tower: the more blocks you have, the more fragile it is. And that is despite Jenga being nicely layered (each block has limited number of direct dependencies).

There are two main ways to decrease fragility:

1) lay out your blocks more carefully.

2) decrease the total number of blocks.

What's interesting, is that most software development practices focus on 1. How to make complex system less fragile? Use a big framework, do unit tests, use static typing, have protected branches, write documentation.

While the biggest payoffs are always in the reduction of blocks. KISS.