> If you also assume that people strengthen their own understanding of a topic if they teach it new engineers don't drain resources In practice I've found this

> If you also assume that people strengthen their own understanding of a topic if they teach it new engineers don't drain resources In practice I've found this assumption is only true if you have very small growth/turnover. I.e. If you hire a new engineer once every couple of years it's probably the case, but if you hire a new engineer every few months it isn't. On average I'd say we have our senior engineers spend 40-50 hours total in the first month teaching/helping a new senior dev. Probably a similar number of hours in the second month, and then it drops to maybe 10 hours/month for the next year. From what I have seen a new senior dev is around 10% of the productivity of a existing senior dev for the first month, 20% for the second, and rapidly reaching 80% by the end of a year. So they are at 1 unit/hour of productivity for the first month and add 160 units of productivity for the month. However, senior devs, at a cost of 10 units/hr, have spent 40-50 hours helping them at a cost of 400-500 units of productivity. Second month they add 320 units but cost another 400-500. By the third month they add maybe 450 units and only cost 100 units. And at this point they have managed to pretty much break even. Of course if you assume training costs are not a real cost but rather beneficial for your existing senior devs then the new senior dev looks productive from the first month. But then you are really just talking past each other.