I once read a book which talked about a thing called agoraphobia.
Perhaps it's that ...

Now if we know that weak spot it helps us in our work.

There are some places he won't go to, and there are some things he can't do--not well, anyway.

I reckon that's useful.' 'Ye-es,' said Macgillivray.

'Perhaps it's not what you'd call a burning and a shining light.' 'There's another chink in his armour,' I went on.