This one actually ties in quite nicely to Mistake #3 (Going Cheap), although it may be the chicken and the egg syndrome - not sure which comes first. Are you going cheap because you're overextending the lifecycle of your technology or are you overextending the lifecycle of your technology because you're going cheap? Because many businesses tend to "go cheap", their first inclination is the old adage, "if it ain't broke, don't fix it". With technology this actually turns out be a more costly approach.
I'm big on analogies and I think all too often too many people think that technology is like operating a car. If you're driving along and it stops working, you simply pull over to the side of the road like you ran out of gas. No big deal. But really, technology is actually more like flying an airplane. You simply can't afford to run out of gas - it's life threatening. While I get that server crashes, data breeches, and downtime certainly aren't exactly life threatening situations (for the most part), they could actually be very threatening to the life of one's business. It's been said that 50% of businesses who suffer a significant data loss are out of business within a year.
Way too often we've seen clients pushing the envelope on how long they keep technology in production (see my blog post on the Really, Really story). These are usually NOT the Best in Class performers in their industries. There's a reason why Dell warranties servers for only 3 years out of the chute. They know their own failure rates. Beyond the cost of dealing with picking up the pieces after a crisis, most of these companies don't realize (or want to even consider) the performance gains by replacing 3 and 4 year old equipment. Because technology continues to improve exponentially, 3 to 4 years is an eternity in performance gains. Just because something's "still working" doesn't necessarily mean it's as effective or productive as it could be - which actually decreases staff productivity. Increasing the performance of a staff member by 5% by upgrading their workstation can bring about a 200% return on investment in a year. Unfortunately, most business owners don't factor the hidden costs into the equation as much as they should.
The most effective businesses leveraging technology these days ALWAYS have a proactive approach to their technology. And overextending the technology lifecycle is NOT a proactive approach. Like I said, you can view technology as though it's like a car or like a plane. It's your choice. Just make sure you pack a big enough parachute if you choose to fly.