Most people do tax planning without even realizing it.
If you knew you would owe tax at the end of the year, and decided to just wait and pay it then, you made a tax planning decision. But tax planning can be much more than determining when to pay a tax that is due. It can affect in what year the tax will be payable to begin with. For example, by pushing income into the next tax year, and accelerating deductions to this year, you minimize this year's tax. In many cases, you can achieve something you want to do in different ways, some of which may be tax-favored.