What does "You can only work on so many things at a time" mean?

Question

From the following context, what does mean this sentence

You can only work on so many things at a time

It sounds to me like

The size doesn't matter both when you work on so many things at a time and when you work on one thing at a time

which is contradictory. WIP in this context is work-in-progress.

You may be thinking that allocating your workload (your capacity) by WIP limits won’t fly because your work items aren’t all the same size. This is an area where size doesn’t really matter because you can only work on so many things at a time. It doesn’t matter how big or small something is when you can only truly focus on one thing at a time. It could be as small as a mouse or as big as an elephant (metaphorically speaking). When it’s done, you move on to the next thing.

Answer 1

So many in this sort of context, means a maximum of - except that it does not specify what that maximum is.

Another (less idiomatic) way of saying it would be: there is a maximum number of tasks that you can successfully work on at the same time.

Answer 2

They probably asked you to have fewer tasks in progress, and said it like this, "you need to be working fewer tasks at a time."

Now there are many reasons and arguments for (and against) fewer WIP items, but they are not English language problems. To ask about those reasons, I suggest you submit a similar question to "The Workplace"