"the feeling something complex might be needed because everything simple was already tried." I feel this hard. Any relatively well known long standing problem

"the feeling something complex might be needed because everything simple was already tried." I feel this hard. Any relatively well known long standing problem I (wrongly?) assume must be impossible for me to solve because so many much more experienced that me people have put many hours of work into it already. But maybe I'm overestimating the actual effort being put into these sorts of things, or the amount of benefit fresh eyes can bring.