I would add that it seems common for task difficulty distribution to be skewed in various idiosyncratic ways --- sufficiently common and sufficiently skewed that any uninformed generic intuition about the "noise" distribution is likely to be seriously wrong. E.g., in some fields there's important low-hanging fruit: the first few hours of training and practice might get you 10-30% of the practical benefit of the hundreds of hours of training and practice that would be required to have a comprehensive understanding. In other fields there are large clusters of skills that become easy to learn with once you learn some skill that is a shared prerequisite for the entire cluster.