Having recently been asked with scoping out what is involved in building/re-building a website for a client I came to the conclusion that the hardest part about building a website isn't the actual construction, it's everything that happens prior to that.
A pretty website is nice to look at, but unless it has substance it's not going to be very useful.
It also goes beyond just substance, it's a balance between substance, structure, and technology.
Without quality substance - there is nothing on the website to keep your visitors engaged.
Without structure - there is no way for visitors to find what they're looking for.
Without technology - visitors end up frustrated and will leave.
I would argue that the priority also follows that order.
Substance without structure is still a useful website. Tools such as Google still make your content accessible, albeit maybe not quite as accessible as you would like if you are trying to keep users engaged with your site.
Substance without technology can frustrate your users, but if the substance is strong enough they will persevere.