"If you design for the web and then port to mobile, you will find that it is really hard to fit your UI onto the small screen." Then don't try make it fit. Try

"If you design for the web and then port to mobile, you will find that it is really hard to fit your UI onto the small screen." Then don't try make it fit. Try designing for it separately, since it's an entirely different experience. If you're trying to work out which order to design in, this is really bad advice, as it isn't one-fits-all. Think of it this way: should the majority of usage happen when we're out and about (native mobile), or when we're sat at a desk (full web)? or do you want to do both in the shortest amount of time (responsive web)?