Probably the biggest surprise I've seen in my career as a team lead is how often people ostensibly work with the team, but actually want to see the team fail. It sounds ridiculous, I know, but it actually happens quite often.

Here are two quick examples where I see this happen often. Let's say you're a vendor deploying software at an organization, and one or more people that work at your client organization originally wanted to write their own solution for this software, and their bosses overrode their wishes, and now they're forced to help implement your software. You need to use those disenfranchised IT people as part of your team to do the implementation, but they'd like to see the project fail, because they told their manager they could do it better themselves. Other variations of this occur whenever someone doesn't get their way, and is forced to go implement things a different way -- now any delays that happen may demonstrate their sage wisdom in not wanting to do it this way.

I've also seen variations on this same theme where a company is working on a product that does what we're implementing, but it's not ready yet. Then a year down the road, when we're doing the final rollout, their product is almost ready, so now they'd like to see us fail. And suddenly the alliance falls apart. Over the last 30 years working in IT, I've seen something like 20-30 variations on this theme.

Lots of times you need to work with people who really want to see your project fail. This came as a huge surprise to me, but I think any senior person should be careful and on the lookout. It's often a significant project risk, and almost always overlooked.