Knowing the reason behind a 10% offering (tithe) from whatever we earned is important as well. It all begin by Abraham, and it continued on from his generation, until what we are doing today. Until Jesus taught about freewill offering, but do not confused this with tithing. They are separated. Tithing is an act of acknowledging God's mercy in your life, for everything that you've earned is because of His grace. On the other hand, offering is an act of love towards God and His churches.
At least, we should be thankful when tithing, and not grumble, even when somebody else ask of you.
WHY? Because you still have the 90% left to do what you want.
At the end, don't we all want to see the promise God made in our lives:
... "and see if I will not throw open the floodgates of heaven and pour out so much blessing that there will not be room enough to store it.
Malachi 3 : 9b