Negligence: Failure to take the care that a responsible person usually takes : lack of normal care or attention
A worrying number of organizations run outdated, unsupported software.
There might have been a time when you could install software and leave it running unchanged for decades. But your IT infrastructure today is much more dynamic and does not allow this hands-off approach. Your client workstations will automatically install security patches and new Java versions, your users will install new or updated browsers, and the evolving security threat makes it necessary for you to continually patch your servers.
The best you can hope for is that nobody gets hurt when your eventually systems crash (that would be criminal negligence that may come with jail time).
Or you can keep your systems up to date.