Stitched-together systems create monster problems

Every retailer with a fragmented stack has four different inventory positions and a policy for which one to believe. The website, store POS, and WMS have ones, and planning does too. Each system is confident. None of them agree, so someone picks a "system of record" and everyone has to trust a number that doesn’t update in real time.

Fragmented architectures produce a strange condition: the enterprise generates more operational data than at any point in its history and can act on less of it. Planning knows the need, OMS knows the promise, TMS knows the plan, and WMS knows when it loaded. None of them know about each other. So, when the customer asks the simplest question of all - where's my order? - five systems answer, and no two agree.

Every stitched-together system has a shadow org chart: the list of people who know how the workaround works and what happens if you touch it. That list gets shorter every year. The workaround does not.

The costliest thing about a stitched-together system is not what you paid for the software. It's what you pay every year to keep it standing. Integration maintenance. Version-mismatch risk. Reconciliation labor. Custom code that someone babysits. Your systems integrator loves this system. Their business model depends on it staying exactly this hard.