Muse endlessly about this, for example (7)
I believe the answer is:
problem
'this for example' is the definition.
(the crossword clue is a problem to be solved)
I can't explain the rest of the clue.
(Other definitions for problem that I've seen before include "Difficulty (these days, of any kind)" , "Quandary or dilemma" , "Brainteaser" , "Difficult matter to solve" , "Question or source of perplexity" .)