It's hard to see most of the time, but Kyren Williams has a really good aptitude for managing to avoid square contact by a tackler. They'll still be able to make the tackle, but the hit he takes becomes more of a glancing blow instead of a direct hit.
That will single-handedly increase his NFL lifetime by a lot. The last guy who I saw with this kind of ability was Thurman Thomas (from those Buffalo Bills Superbowl teams), who wasn't a big guy at all, and managed to last a long time in a hard hitting league.