Unanswered Prayer

Justin Dillehay provides four possible reasons here. Another reason could be sin. A number of passages might support this (e.g., Ps 66:18; Prov 28:9; Isa 59:2; 1 Pet 3:7). Whether texts like these refer to a deficiency in praying or God's unwillingness to answer but in either case the net result is the same.