A problem shared is a buck passed.
Somebody Wise
Many years ago, I was playing a rugby match and missed a crucial tackle. The now-free player started running, unopposed, towards our tryline. And in the chaos of the game, our captain shouted to me "he's your man - chase him down." At that point, I was on the ground, hoping somebody else would pick up the tackle. But being named gave me no choice... I had to tackle him on the second attempt. I ran back and made a try-saving tackle. Disclaimer: There is an excellent chance he scored. I mentioned this was long ago... but my sporting prowess is not the point of this post...

There are a few things that cause alarm bells to ring loudly in my head. And, if I'm focused on delivery, one of the massive alarm bells will be when somebody says "they'll do it". And they is not a singular person.

You're in a meeting, and there is a dependency on something new being done. And somebody (please tell me it's not you!) says "Group IT will do that". And you move on.
Congratulations. You've just introduced a weak link.

Projects are all about team work. We're all a part of the value chain (excuse the pun). But, they're also about accountability.
So, when I'm being particularly aggressive, and somebody says "Group A will do that", my answer is always the same...
"That's great. But... who is the one person in Group A that will report to us, own the progress and their resources, who has the mandate, and who get's fired if they don't deliver for us, on time?"
If you can answer the above question with one person's name, then:
- You don't have a weak link and
- You've just extended your project team with a powerful ally.
It's human nature to palm off problems...
- We've mentioned that Group A will execute;
- I'm not in Group A
- I'm off the hook!
(Put another way - and I just did this myself at a professional level 5 minutes ago... when somebody has a list of 20 items to be worked on, and there is a column which says "accountable" - I can guarantee you that every recipient only scans the list looking for their name...)
Summary
- Sure, there is no "I" in "Team" - we all need to work together to deliver.
- But, if you want to have a better guarantee of deliver, for every task, you need a single accountable person.