He praises React because it makes it easy to change the UI design at any time in response to new requests from the designers.  The hard parts he talks about are animations, pre-loading, and virtual rendering, which require some higher level orchestration to get right in any framework.  You have to have some component keeping track of this stuff.  They mentioned that they had to extend the standard transition component to make it more reliable.<p>He also talks about writing code in a way that will work on both the server and client side, which is something you have to think about no matter what library you&#x27;re using.