The RISC OS start-up sequence is not overly complicated compared to some systems, however if you don't know your way around it, it will look like a maze of twisty passages, all alike.
RISC OS also suffers from the problem that errors are passed back up to the operating system as nothing else catches them (it is a set of Obey files, akin to .BAT files in DOS parlance). While this might seem useful for error reporting, it isn't so useful when the boot aborts and you are thrown into the Desktop without knowing what has and hasn't been done. 

Harinezumi is a boot script processor. Essentially you run Harinezumi instead of your normal boot file (that's $.!Boot.Utils.BootRun). Harinezumi will then use your boot file (the BootRun) as a script of what to do. It will vet stuff where necessary, and mimic all of the things the BootRun would do.