I had a strange and persistent difficulty unlocking my front door. (discovermagazine.com)
Are you sad, overwhelmed, or having persistent difficulties in your relationships with others? (theravive.com)
It is just such persistent difficulty with the English language — particularly with reading and writing — that led 63 parents to endorse the strike after a series of letters, verbal requests and parent petitions demanding English - only classes produced no results. (onenation.org)