One of the biggest causes of slowness is just waiting for web requests. The fact that so much software is either online or built using the same stack even if it isn't, puts all that software in this blocked/waiting state constantly while using it.

Anyone not in the US feels this even more since so much online is US hosted, 300ms for every little interaction adds up quick.

If your software has the affordance of a waiting dialogue or loading wheel for many of its UI controls, you are building with this default blocked assumption. Even if you are building something web based, ask yourself if that's actually necessary for your software or if you could build it differently to avoid constant UI blocking.

It's not very hard to engineer software with these two constraints at the same time:

* Must feel very responsive * Network requests can take up to 500ms end to end