The next element of the method is critical - the current quantity of any resource
is not 'caused' by any other factor, but is mathematically identical to the sum
of everything ever added, minus everything ever lost. This is easy to see in the
case of cash:
Cash-today is equal to all cash that was ever received,
minus all cash that was ever spent
But this is equally true of every other asset-stock, i.e.
resources. The number of customers today is equal to every customer that was ever
won, minus every customer that was ever lost. There is
no other reliable explanation for that number. It cannot be estimated
from marketing spend, price levels, number of competitors or anything else, because
it is 100.0% explained by historic gains and losses - and if you can't explain 'customers'
with other factors, then you can't explain anything that depends on customers either,
e.g. revenues and profits! Following the same logic, today's staff is the sum of
every person ever hired, minus every person ever lost. Today's product range is
the sum of every product we ever launched, minus every product we ever discontinued.
This is why today's performance and future performance are both unavoidably dependent