JanuaryA scope is agreed over email and a call. Fee, stages and what is excluded are all in there somewhere.
FebruaryThe work starts. Two extra requests come in and are absorbed, because refusing felt awkward and there was nothing to point at.
MarchThe invoice is raised from memory of the original fee. The extras are not on it.
AprilThe client queries a line. Nobody can produce the agreed scope quickly, so a credit is issued.
SeptemberThe balance is still outstanding, the partner is chasing it personally, and it is the fourth such conversation this month.
What it actually costsWork delivered, absorbed, invoiced late and then discounted
None of these are accounting failures. They are all failures to have written something down in a place both sides can point at — which is what a quotation and an activity timeline are for.