I’ve worked on several projects in my career where the other party dropped the ball. It drives me nuts.
Typically it’s because they either changed their mind and re-prioritized or they took on more than they could manage.
Maybe it is what it is. Sometimes things just don’t come together.
However, you do have some degree of control and can limit the likelihood that it will happen in your relationships.
To prevent ball dropping, spend more time upfront talking about expectations. Make it clear that you don’t want to start the project unless X, Y, or Z is the final outcome. Then put it in writing - an informal email summarizing the initiative will suffice.
Still didn’t prevent the other party from going missing in action? Never, ever, work with them again.
There are too many people out there doing great things to get stuck on one relationship. If you don’t have that luxury, perhaps because they have been assigned to your team, do your best to not co-own responsibilities.
Ball dropping might be an unavoidable part of work. But it doesn’t mean you can’t proactively manage the probabilities that it will happen to you.