The following is human logic:
I should donate either all (except of remaining to eat and other basic needs) or none of my salary, because my projects are either less important or more important that the projects I donate form. If my projects are more important, I should use all me money to support that projects. And if my projects are less important, then I should dedicate all my money to others’ projects.
For example, I am a wise mathematician and thus my projects are more important than projects of any other man or woman I know. Thus I conclude that I should not donate anything, but use all my money to support my important projects.
The above does not entirely hold for a businessman (rather than a receiver of a fixed salary or other fixed kind of income), that is a person whose income depends on his spends (the more he invest the more he receives). A business should decide a percent to spend for a charity and percent to spend for investment to earn more money in the future to spend more for charity in the future.
I nevertheless pay a tithe in a church. Why? Accordingly the above I should spend all my money to support my scientific activity.
God wants us to pay a tithe. If a man spends all his money to his own projects, he doesn’t rely on support of God. We should pay to God and expect that he will return us back more money.
“I am so great that I should not donate anything” stance is wrong accordingly Bible. We should rely on God not to ourselves. I we consider ourselves too great to donate then we consider ourselves above morality. Nobody is above morality because everyone should be subject to God.
This is because a talented and powerful but greedy person is even worse than nobody. The economy on the Earth is just a part of the economy of the entire universe ruled by God. I we are a part of heavenly economy, then we must subject ourselves to God and thus donate (at least a tithe) relying that God will give us back more.
If we think that God should help our projects without us donating to others’ projects, we are in pride. Bible says that God resists proud. We should take this resistance into account calculating our spends and gains, because if we don’t, God resistance will disturb our projects.
My projects are more important than yours. Donate all your money (or at least how much you are willing to donate) to me.