windows 7 update question

From: Windows Updating Explained ( this is a direct link which will download the .docx document )

Downloading updates

Once the Windows Update client determines which updates apply to your computer, it will begin downloading the updates, if you have selected the option to automatically download updates. It does this in the background without interrupting your normal use of the computer.

To ensure that your other downloads aren’t affected or slowed down because updates are downloading, Windows Update uses the Background Intelligent Transfer Service (BITS) technology which downloads updates using idle bandwidth. This technology ensures that Windows Update downloads only when no other active download is in progress on the computer. This allows you to smoothly carry on day-to-day activities even while updates are being downloaded in the background.

Windows Update also supports pausing and restarting downloads. You do not have to worry if you need to shut down your computer, or if you have lost your Internet connection while an update is downloading. Once the connection is reestablished, the download will continue where it left off.

That's the official Microsoft explanation of pausing/stopping/restarting automatic update downloads.

In reality, if there are a sizable number of updates being downloaded ( say, 25 or more ) then there is a chance that components of the updates, known as packages, may become corrupted.

If one of the updates fails to install do not repeatedly try to install it. Repeatedly being more than 3 times.
Instead, open Windows Update in Control Panel.
Click the View update history link.

Click on the update that is showing Failed under Status choose View details.
Towards the bottom of the window there's a link to a Microsoft Knowledge Base article for the update under More information:

There will either be a direct link to manually download the update on the KB article or, if this is a Security update, a link towards the top of the page for IT professionals.
That link takes one to the Security Bulletin for the update which contains links to download said update from the Microsoft Download Center.

Manually downloading an update that fails to install eliminates a couple of factors that could be the cause of the installation failure.

2 such factors being an interrupted download of a sizable number of updates and file corruption in the location where Automatic Update stores the downloaded updates.