When you withdraw from a retirement account, the account administrator is required by law to with hold a minimum of 10% for taxes. Most of that time, that's the exact amount that will be with held. For some tax payers that's just not enough to cover the complete tax liability when considering all of the person's taxable income from all sources.
On top of that, if it's an early withdrawal the account administrator is required by law to with hold an additional 10% for the early withdrawal penalty.
