Here's why:
* Semicolons connect two independent clauses (complete sentences) that are closely related. The two clauses in your sentence are:
* "Lastly the other trait you possess is willpower"
* "Should I use a comma or semi-colon?"
* Commas are typically used to separate items in a list or to set off introductory phrases. They don't work in this case because the two clauses are independent and need a stronger punctuation mark to connect them.
Corrected sentence: Lastly the other trait you possess is willpower; Should I use a comma or semi-colon?