First week
First week: a fleet account sends three units in for brakes, tires and a transmission job. Good work, the kind you want more of. You order parts on Monday, your techs turn the wrenches by Wednesday, the invoice goes out Friday with net 30 terms printed on it, same as always.
Second week
Second week: the parts bill from week one lands. Payroll lands, it always lands. A retail customer pays cash on collection and the till breathes for a day, then the alignment rack throws a fault and the landlord's increase letter arrives in the same mail.
Third week
Third week: the fleet account's accounts payable department is perfectly friendly and perfectly clear that the cheque run is next cycle. Your invoice is approved, it is coming, it is simply not here, while everything you owe is here already.
Fourth week
Fourth week: you do the arithmetic every owner of a working shop knows by heart. The business is profitable on paper and short in the bank, at the same time, for reasons that have nothing to do with how well you run it. That gap, between work done and money landed, is what working capital exists to bridge.