The purpose of doing this is to prevent those how don’t know from guessing. In saying that though, an educated guess is only as good as the education, and this may help in that.
Riding motorcycles at any level you will come across problems with your bike at some point, unless you have no limit on your funds, and you throw it at the problem. However you may need or want to be able to diagnose a few things, that may be what’s causing the issue.
My education is my own experience (and my mates bikes). I will disclose some of the less obvious things that can go wrong, some may be specific to a certain type/model of a bike or brand, I will try to define if this is a case.
I am aware that the internet is awash with this sort of information, how ever it has proven to be less than accurate on occasions for me and has even cost me more money than what it would have have if I had guessed. The best source of information is a Haynes manual or Clymer Manuals. Personally I find Haynes to be better, but I guess that’s what I have grown up with, both offer factual information and will save you money and time in the long run. You can often look about the auction sites as they often have manuals on bikes that people have sold and are left with the manual.
I hope this is going to be a little help.