Something which I've only grasped fairly recently is that it's sometimes NOT best to stick rigidly to the rules regarding technique.

Yes, it's important to learn them but also useful to break them from time to time. Quite often the standard forms of fingering(applies to all instruments) just don't work very well on certain tunes or they feel very awkward. So, if something slightly different works better for you on a particular piece then why not? As long as you are aware of what you are doing and not just slipping into bad habits of course....

This revelation came to me when learning the harp and, to a lesser extent, the piano accordion, where you have to "plan ahead" as regards fingering. Depending on how the tune is arranged there are many different possibilities(not all players necessarily choose the same fingering although there are some basic rules). I then started to think a bit more about what I was doing on the mandolin and fiddle..although with most tunes the fingering still comes naturally, it does help with the trickier ones to try something a little different.