Which areas of rationality are underexplored? - Discussion Thread

There seems to ac­tu­ally be real mo­men­tum be­hind this at­tempt as re­viv­ing Less Wrong. One of the old­est is­sues on LW has been the lack of con­tent. For this rea­son, I thought that it might be worth­while open­ing a thread where peo­ple can sug­gest how we can ex­pand the scope of what peo­ple write about in or­der for us to have suffi­cient con­tent.

Does any­one have any ideas about which ar­eas of ra­tio­nal­ity are un­der­ex­plored? Please only list one area per com­ment.