How to solve a difficult problem (which has been stuck for a long time) and understand the same concept for a long time...
I'm aware that there could be problems that frustrate people severely and remain unsolved for a very long period. (Please respond.) how to fight such problems....
look to editorial and try to learn about category of the problem
If you have the ability to solve it, use what you have learnt to solve.
If you really don't have the way to solve it, give up appropriately.