Why do financial models always betray you at the assumptions stage?

Like seriously… it starts off all clean and beautiful. Proper structure, nice formulas, everything makes sense. You feel like a finance god for a moment.

Then assumptions enter.

You add a few growth rates… then costs… then pricing… then “just one more scenario”… and suddenly the whole thing starts acting weird.

Numbers stop matching, links get confusing, and you’re scared to change anything because something somewhere might break.

And yes… a few things may or may not be hardcoded “just for now” (we all know what that means).

The real pain hits when someone asks, “Can we tweak this assumption?”
And you’re like… “yeah… but also no.”

how do you guys keep your models from turning into chaos once assumptions kick in?