Apple Watch Series 3 update

FWIW, a lot of people have problems updating a series 3 watch due to insufficient memory. In some cases, unpairing the watch, completely erasing it, then pairing and restoring the backup will resolve the issue after an update. (Simply unpairing and pairing again may not work.)

Unpair and erase your Apple Watch - Apple Support

Also, see fireyjack's reply to:

Can't update her series 3 watch. - Apple Community

I have always had to unpair my watch, perform unspeakable magical incantations at midnight, hop on one foot and sacrifice a rubber chicken to get an update to go onto my series 3.

Except today.

Today, it updated just like you would expect any other apple watch - I hit "update" on my phone and watched in amazement as the blasted thing updated to OS 8 right before my eyes.

A sure sign of the end times...