The phrase "strongest thing" means something that has more power or force than anything else.
Sentences with «strongest thing»
This seems like quite the mix of dogs, but they have one very strong thing in common and that is their primitive nature. (themoderndogtrainer.net)
I actually haven't liked how strong things have been when I've used the dark cocoa, but these brownies were very good since I used some of both kinds. (bakingandboys.com)