The last straw if you have only one pencil (8,5)
I believe the answer is:
breaking point
'the last straw' is the definition.
(I've seen this in another clue)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for breaking point that I've seen before include "The end of one's tether?" , "Moment at which something gives way" , "Critical moment for collapse" .)