not enough inward travel for focus

What is the reason an eyepiece cannot reach focus, because of not enough Inward travel? What can be done to remedy the situation?

Thanks, Carol

Couple other ideas:

If its a 1.25" eyepiece in a 2" focuser that has
trouble, you can get various 1.25" adapters where
the eyepiece sits very low or even inside the
2" tube.

If you only need a couple millimeters, you can
put clear or UV filters on the eyepiece. You
will get about 1mm effective in-travel per filter.
If you need more than a couple mm, you can make
yourself a filter with a thick glass window, but
it is more work.