[tlug] How can my computer forget to do stuff sometimes?

[Dave M G <dave@example.com>]

TLUG,

I run Ubuntu Lucid, with the Gnome desktop, in combination with Compiz 
and Emerald. If you're not familiar with any one of those, it's not 
really that important what role each of them plays. Altogether they run 
the GUI interface, each application manages different tasks.

80 to 90 percent of the time, when I boot up the computer, they all 
load, they all work, and everything is great.

But now and again, I boot the computer, and something will be off. For 
instance, the Emerald window manager won't be on, so my windows won't 
have any frames on them. Or sometimes recenly the little icon for 
rebooting and restarting the computer is missing from my Gnome panel.

About five to ten percent of the time, there's some small issue with the 
interface. Sometimes I reboot and its fine. Sometimes I just have to 
start the particular program that's not functioning.

What confuses me about this is that I don't see how anything can vary 
from boot to boot. As far as I understand it, when the computer boots, 
it runs through the same list of tasks to start things up, in the same 
order every single time.

So if, for example, Emerald didn't load one time, simply rebooting 
shouldn't fix it. It should remain off every time.

Or, if it works, it should work every time.

The whole point of computers is to execute tasks exactly the same way 
each time.

I'm not looking for a solution so much as I'm just curious. How can it 
even be possible for a computer to overlook a task every now and again?

--
Dave M G