# Why is {a} not transitive unless \$a = emptyset\$

I am trying to understand what transitive sets look like or what not transitive sets look like. I found another thread where someone stated that $${a}$$ is not transitive unless $$a=emptyset$$. I don’t quite understand why this is the case. Off course $$a in {a}$$. But why is $$a nsubseteq {a}$$
(Source).
I have seen a video on YouTube where the guy stated that $$F={F,G}$$ with $$G={F}$$ would be transitive.
Those seems contradicting each other to me… (Source)