We’ve got a severe problem at my company. Management doesn’t want to invest the time or resources to developing a standardized training manual, training material, or even a Lessons Learned catalog, and everytime we get a new employee it’s like 6 months of them slowly picking things up before they are useful and probably a year and half before they got comfortable in their role.
Did any of you have this hurdle? And how did you get management to finally listen and invest the resources to do this properly?

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I’d suggest framing this as a solution. Such as: before you begin the task, I need x hours to create some notes of the procedure and links to the certification docs. Oh btw I made it as a template so next time we can duplicate this file and fill in the blanks.
Same with newbie: oh I asked the newbie to take written notes, because it’s very common for a new hire to ask the same question multiple times until they get independent. Oh btw the next hire can just read and tweak these notes. No, it doesn’t completely replace me supervising them, it just makes it faster. Etcetc