Two opposite poles

Growing up, my sister and I have always been quite different. This included our personality, temperament, tastes, likes/dislikes, interests, etc. As a result we clashed often, fighting like cats and dogs.

The only times we did not fight were when we were busy planning surprise "party" or gifts for my parents. However, they eventually stopped being surprised because the minute they saw us acting like "angels", they immediately figured out we were up to something.

Here are few examples of our differences:

Sister/Me

vanilla/chocolate
healthy food/ junk and sweets
classic lit/novels
no animals/dogs
reserved/open book

I could list a lot more but you get the idea.

One day, I asked my sister, instead of pointing out our differences, what we had in common. I said that there must be at least ONE thing.

She pondered for a moment then replied.

"Our parents."