Do we need wide knowledge?

About 10 years ago I worked as team lead on a project for government client. We had Project Manager who enjoyed drinking coffee often. I wasn't experienced in project management back then.
PM said we work in Agile way. Our client said we have a concrete deadline.
See the problem already? Then you're very good 👏

One day I was thinking "Hm, we have the scope of work changed again but deadline is the same. How does it suppose to work?".

Few more days passed and our PMs ran on vacation without telling anybody (probably to drink more coffee he couldn't find in our office).
Our client was very worried the scope of work won't be completed on time.
Devs were heavily stressed trying to meet a moving target.

In the end I went to the client and honestly discussed our situation. The client got the point and helped me to drive project further helping with the scope and deadline.
We both knew the source of our problems was in our bad coffee, otherwise our PM would manage things 😜

Months later I had to leave this company for security reason. What was a reaction?
Our coffee lover tried to frighten me. Our client offered me a job to work for them directly - the best sign of client satisfaction.

What was the first thing I did on a new working place?
Completed several trainings on project management to understand how our project should be managed normally.

I strongly believe being familiar with all details surrounding your work is important to succeed in your work.
Lack of knowledge is compensated by pain, mistakes and failure.

Too much knowledge is something that blocks real doings. But that is another story...