For many celebrities, Throwback Thursday this week was a chance to reflect upon the sad memories and remember those who lost their lives on September 11, 2001 -- 13 years ago to this day.

But for others, it was a reminder that we, as a society, persevered, and that the daily joys and little pleasures of life can't be taken away from the human spirit. Here is a look at some Throwback Thursday posts from our favorite stars.

Demi Lovato confesses to sneaking into a department store with boyfriend Wilmer Valderrama to take a quick nap! Ha!

Reese Witherspoon shares a photo from her second movie ever, 'Wildflower.'

Calvin Harris kicks back in a dressing room.

Julianne Hough shares a pleasant photo taken in Canada.

Coldplay reminisce about a 2008 concert in France.

Anna Camp from 'True Blood' caught her pooch in the act of destruction.

Tegan and Sara share an adorable photo from when they were kids!

Chris Kirkpatrick's regrettable haircut.

Travis Barker remembers working with A-Trak onstage.

Michelle Rodriguez pays tribute to Paul Walker and the cast of 'Fast & Furious.'

Jack Black shares his first headshot photo!