I tend to work on the theory that you actually need at least N+1 guitars in your collection so that you don't then end up with N non-functional guitars due to such things as broken strings and etc, but then you also need to factor-in Entropy (Randomness) too, this can take the form of having to play a gig at short-notice, or a mate needs to borrow a guitar from you cause his band is playing at his sister's wedding, or some other special occasion, and his guitar is currently being worked on due to some random reason.
The same theory could be applied to things like sets of strings (it's a pain when you break one, or more, of the strings on your guitar and you don't have any more spares, and the music shop is closed cause it's Sunday afternoon), even amps are not immune to the above theory, something as mundane as a 9V battery is also subject to the above theory as well, basically when deciding how many of a certain thing you need, always err on the side of one extra.
Last edited by DrNomis_44; 11-12-2016 at 12:48 AM.