Retirement tax questions

I read some articles if we do not take action to withdraw excess after 10/15 in the following year,  when we remove the excess later, the excess will be considered the income and we are due for double taxation.  I did not see this portion being mentioned.  Could you please help clarify that ?

 

From IRS : Unless timely distributed, excess deferrals are (1) included in a participant’s taxable income for the year contributed, and (2) taxed a second time when the deferrals are ultimately distributed from the plan.