…to avoid the errors in your SAP® RE-FX system nobody can explain later.

The posting run finishes and I wait — not to see whether there are errors, but how many. A handful of contracts never post correctly. I stopped trying to fix the root cause; I maintain a personal list instead. The accounts team even asks why I wanted to adjust the debit position once. I usually spend eight hours tracing mistakes. Sometimes I find the reason. Sometimes I say “I’ll monitor it next month.” Next month, it might be a different building.

And then there’s the other kind of problem — the ones that don’t come from the system itself but from everything that happened to it. A migration nobody validated afterwards. A reorganisation that moved contracts to a new company code but not cleanly. A regulatory change implemented under time pressure and never reviewed. None of these are bugs. All of them leave residue — small inconsistencies that compound silently until someone notices a number that doesn’t tie.

The overall lease liability changes slightly every month. A few hundred euros here, a rounding difference there. I’ve never established whether this is correct behaviour or something drifting. I asked on a forum once. Someone replied with a note number. I applied it. The changes kept happening. I assumed it was correct.

There are things in my configuration I’ve never touched because they were there when I arrived and they seem to work. One condition type is called “Z_REFX_CNTsomething” — clearly custom, clearly from the original implementation. It fires every month and posts something to an account. The account reconciles. I’ve ask the developer: he said it has to do with the BAdI of the Indexation. I’m not sure I want to know more.

When auditors ask “are you confident this figure is complete and accurate?” I say yes. Inside I’m thinking: “I’m confident it’s produced the same way as last year. Is that the same as accurate?”

There are reports I do not question. Numbers I do not drill into. Not because they look right — because I do not know how they are built. My team tells me they tie out. I trust them. But the same question, asked twice, sometimes gets two different answers — both reasonable, neither traceable. If the monthly close ties out, I sign it. What sits beneath the figures is a black box I have learned to live with.

When someone proposes a change — “should we restructure how rent and service charges are booked?” — my first reaction is hesitation. My team is confident it can be done. I have learned that “it can be done” and “we will know what it costs us downstream” are not the same sentence. How many reports depend on this? What will I have to re-explain to the auditor? I usually park these conversations. Not because the question is wrong, but because I cannot estimate the cost of the answer.

I sense that some numbers behave oddly. Service charge accruals look smoother than the underlying data should allow. When I ask, the explanations come — technical, plausible, complete. And yet the gap between what is explained and what I see does not close. So I leave it. And every quarter I sign off something I do not fully understand.

At some point I stopped asking whether the system is really right and started optimising for getting through the month. Admitting “something fundamental might be off” feels like opening a door I cannot close again — investigations, projects, blame, expectations I do not have the bandwidth to carry. As long as the numbers do not look obviously absurd, they are good enough.

Meanwhile I and RE-FX grow around each other. My routines, my spreadsheets, my unwritten rules wrap themselves around its quirks. The strange things become “just how we do it here.” I do not document half the workarounds because I remember them. I do not challenge odd results because I have internalised the explanation. I am the missing manual.

The cost of real change quietly explodes. Fixing the system would now mean not only touching SAP, but unpicking years of tacit knowledge and unwinding the personal logic I have built on top. The system is not just complex anymore — it is personal. It runs on my memory, my judgement, my workarounds. If I leave, no documentation can replace what I have absorbed. If I stay, I keep paying the cost in silent overhead — every month a little more.

The only way out is the harder one: see it clearly first. Not fix it, not blame it, not justify it. Just see it…