Anything can be done once, twice, or three times, but that doesn't mean it's repeatable; an essential concept in any business. What do this word mean and why is it a core concept? OK, now apply it to marketing.
Repeatable: the ability to perform an action or produce an outcome virtually an infinite number of times without the predictable loss of quantity or quality. Business processes must be repeatable or the operations will have variation. Variation is good if you are an artist trying to produce unique masterpieces, variation is bad if you are trying to control costs and maximize ROI. Imagine if every time your accounting department balanced the company accounts differently, or your marketing team changed the logo slightly every time they created an add, or every time you bought eggs you got a different quantity. Repeatability is a measure of variation from cycle to cycle over a defined time frame and is controlled with procedures, training, in some cases equipment or tooling, and raw material uniformity to name a few.
How does this apply to marketing? If the raw material, i.e. lead quality and quantity vary from day-to-day or person-to-person, then the quality and quantity of the sales produced (product) will vary as well, which would ultimately make comapny growth projects impossible, budgets meaningless, and long term viability difficult. Bottom line is to make any process successful a key factor is it's repeatability and the best way to establish it is to know your process, implement the appropriate controls, and monitor the right metrics.
-Ghen Sugimoto