12. Putting too much faith in one vendor
It's easy to see why some companies keep going back to the same vendor to fulfill all manner of IT needs. Large IT vendors love to offer integrated solutions, and a support contract that promises "one throat to choke" will always be appealing to overworked admins.
If that contract has you relying on immature products outside your vendor's expertise, however, you could be the one who ends up gasping for breath. Rarely is every entry in an enterprise IT product line created equal, and getting roped into a subpar solution is a mistake that can have long-term repercussions. Giving preferential consideration to existing partners makes good business sense, but remember there's nothing wrong with politely declining when the best-of-breed solution lies elsewhere.