Last Saturday my wife and I went to a cafe for breakfast. It was mostly empty. One employee was showing another how the till (cash register) worked.
Then she showed her which options linked to which menu items, how to serve customers, where to sit customers, which tables referred to which customer numbers, what food items were/weren’t available, what time they opened, what time they closed, how to handle customers with limited English, the different types of tea, what taxes she had to pay etc etc…
You get the idea. The new employee was completely frazzled and drowning in information. Customers could see it, the service was slow, and the experience was bad for all involved.
Most teams are like this. They add a newcomer to the project and then overwhelm him/her with a huge amount of information in a short amount of time. The newcomer is expected to acquire years of knowledge in a day or two.
On my first day in one of my first jobs, I was taken to a meeting room upstairs where the entire team went through every project for every client while I scribbled notes (and pretended to understand the vocab).
It doesn’t lead to a great first day for the newcomer and not a great return for the project. Ever heard stories of employees quitting on the first day/week? This is why.
If you’re adding a newcomer to the project, give them a small piece of work, the right amount of information, and let them get to grips with it and produce something good. Do everything you can to make them feel like a competent, productive, member of the team as quickly as possible. Gradually expand from there.
Like adding someone to a community, giving someone too much information too soon leads to bad results. Maintain a high level of competency and expand steadily.