Here's how a storekeeper makes sure the store is working: She sits at the register and watches.
If the line is twenty people long and folks start walking out, she hires another cashier.
If too many people pick up a new product and then put it back on the shelf, she asks for new packaging, or drops it from the inventory.
If there's a line outside in the morning, she opens earlier.
Alas, the same feedback cycle doesn't happen automatically online. You have to build it into your website–if you don't, the silence may confuse you. If you have no idea if people are walking away in frustration, you can't possibly fix it.
This gap is surprising, because the web is a direct marketing medium, and direct marketing is obsessed with measurement. When a direct marketer comes back from the post office, she knows precisely how much she spent, and how many orders ended up in the PO box as a result. The web can work that way (but only if you let it).
Consider the poor airline business, now generating almost all their revenue via online sales through websites that confound, frustrate and perhaps drive people away.
How much does it cost when someone can't figure out how to print the boarding pass that may or may not have been generated? Or is forced to re-enter a form several times because the airline tried to upsell insurance without defaulting to 'no'? Or has to do it all over again because the autoform feature is broken and the site isn't smart enough to understand a zip code? Or my most/least favorite: because the buttons are the wrong size and the wrong shape and color?
It's usually not the designer's fault. It's politics, committees and compromises made in the absence of daily, real world feedback.
What would happen if an audible bell on the desk of the CEO rang every time one of these things caused a ticket to not be sold, or a form to be needlessly reloaded?
What's not working for you–that you're not measuring?
We're good at fixing things once we know they're broken.