That's a pretty weak excuse that would raise serious concerns if one of my managers said it to me. The job of a manager is to debug these kinds of things, and

That's a pretty weak excuse that would raise serious concerns if one of my managers said it to me. The job of a manager is to debug these kinds of things, and frankly, distinguishing between technical gaps and personal issues is the easiest form of this. That's not to say you never get it wrong, but you listen, adjust and course correct.