He's good at solving all sorts of knotty problems.
Tips
usage
Originally a medical term (疑 doubtful + 难 difficult + 杂 miscellaneous + 症 symptoms). Now extends freely to any stubborn technical, legal, or administrative problem. Very common in business IT and repair contexts - 'tricky edge cases.'
memory
Break into pairs: 疑难 (doubtful + difficult) + 杂症(miscellaneous + symptoms). A symptom you can't easily pin down or classify.
