The difference between legalism and true self-sacrificial obedience, or "kingdom living" is that legalism is all about what you do and "kingdom living is about where what you do comes from" (I'm not sure if it was Keith Matthews or Dallas Willard who said that).
So when it comes to generosity, we should not be nearly as concerned with keeping track of how much or how often we give of ourselves, this is quantitative generosity, as we are with the qualitative and unmeasurable elements of our giving. Our ultimate endeavor when it comes to this is not that we be more outwardly generous but that we genuinely become generous people in our hearts.
The important thing is not that we give but that we are giving individuals. But, on the flip side, a statement such as that of the previous sentence can easily be manipulated in our minds into a lie. We can easily use this mentality to justify inaction. Someone might say, "I don't need to give money to that person in need because it's not about what I give, it's about how generous I am." Generosity of heart is meaningless and, in fact, not true generosity if it stays in the heart. If our generosity does not make it from our hearts, to our hand, and eventually to our wallets, then it's worthless. Our beliefs and our inner qualities are not secrets. Our true inner qualities and virtues will become blatantly obvious to anyone who watches our lives. Generosity is something you do with your hands. So someone should say, "I will give to that person in need despite the fact that I have already given plenty this month." True generosity will never paralyze someone from giving, it should never become an excuse not to give (as legalistic giving sometimes can). In fact, on the outside, legalistic giving and true generosity might look very similar on the outside except that true generosity doesn't stop at 10% if it doesn't need to.
The true secret to unrelenting generosity is to actually give.