Our reactions to page delays have specific time increments:
0.1 seconds gives us the illusion of instantaneous response.
1 second keeps our flow of though seamless.
10 seconds keeps out attention, just barely.
After 10 seconds, we start thinking about other things, making it harder to get back into our task when the website finally responds.
If you design a site that makes users feel out of control, they will not care about completing their goals on your site.