I'm a proponent of self documenting code (method names, variable names, immutable variables etc) but this only helps document the WHAT and sometimes HOW but sel

I'm a proponent of self documenting code (method names, variable names, immutable variables etc) but this only helps document the WHAT and sometimes HOW but seldom the most useful WHY or WHY NOT or what I have tried before this and what didn't work so I changed it.