Simply put, causality would imply that the cause is a sufficient condition for the effect.
That A caused B would only mean that A is a sufficient condition for B -- not that A is a necessary condition for B. This is because there may be other things that can bring about state B. For it to be a necessary condition, it must be the only condition that can bring this about.
So considering your example with a bit of variation,
I had $40. Now I have zero.
This current state of having zero can be caused by an of a number of sufficient causes:
- I lost the $40 in a bet to you
- I spent $10 on one thing and $30 on another.
- I bought 40 things that cost $1 each
- My money was stolen.
etc., etc. Any of these is sufficient for me and my money to part.
Second, causality is a slightly different notion than being either logically necessary or logically sufficient. Necessary and sufficient refer to the relation between statements and do not (necessarily) imply causation between the two things.
Person X is my wife is a sufficient but not necessary condition for me being married. But in no way does this mean that "me being married" is the cause of "X being my wife."
To make it causal, we can
say I married X, therefore X is my wife.
An important distinction between that and the above one I said was not causal is that we now have a temporal sequence.
For much more on causality, see the SEP entry.
Maybe to summarize:
- Causality is different from necessary/sufficient in that the former is a metaphysical relation between events (more than but related to the sequence of events) and the latter terms are about logical conditions.
- The cause of something can be said to be sufficient to the effect.
- The cause of something is not (normally) necessary to the effect.
- Something can be necessary or sufficient with respect to something else without being its cause.