What is it that separates a manager from a non-manager? Is it skills? Experience? Age? Brown nosing? No, it's none of those things. Or at least, it shouldn't be any of those things.
What separates a manager from those who aren't managers is the willingness to make a decision, and to be comfortable with that decision.
Yeah, that doesn't sound like much of a difference, does it? But oddly the important part is not even the willingness to make a decision. Lots of people are willing to make a decision, or so they claim. Many, many people talk the talk, but when it comes to walking the walk, especially for a decision that could have business ramifications or requires other people to do things, they suddenly develop cold feet and come up with a reason why they shouldn't make that decision.
Some of the people you know who are managers, according to their title, will be like this. They'll have to make the decisions because that comes with the job, but they'll put the more difficult ones off until they absolutely can't avoid it, and when they do make them they'll be defensive about it and irritable about the outcome until they're certain things haven't gone wrong. They may even delegate the decision-making responsibility to a member of their team, and then use that person as a human shield if things go wrong. "Well Joe made the decision, and he IS the technical expert." Or the horrible, insidious "I trusted Joe and he let me down. It's my fault, I shouldn't have given him the responsibility.", thus throwing poor Joe under the bus whilst simultaneously playing the victim. Urgh. (If you've ever worked for that kind of manager, this will be familiar. If you still work for that kind of manager, get the hell out before your career at that company is tainted by their sly putdowns and gradual breaking of your self-esteem.)
This is why being comfortable with dealing with the consequences of a decision is the most important factor. When you're not scared of the ramifications, when you believe in your judgement, decision making is easy. That doesn't mean it's always quick, and it doesn't mean the decision itself is always an easy one. It might take quite a long time to come up with a decision, especially for a contentious one where there are 2 (or more) opposing schools of thought on a subject. But the act of making the decision will be easy, and the feeling afterwards will not be one of terror or dread. The manager who doesn't trust themselves, or doesn't have the technical knowledge to understand the import of the decisions they're making, will be the ones who throw their staff under the bus. A manager who trusts their own judgement and has a decent handle on the important parts of their area of responsibility is much less likely to do this (Although, some people are just terrible human beings. But we're not talking about that here).
It's ok to be worried about what will happen when you make a big call. That's human nature. But it's a rare management decision that should keep you up at night. Decisions have to be made. Sometimes very important decisions. Being able to make them and then explain them to others afterwards is a key part of management. As you go up the chain of command and do less managing and more leading, decision making becomes even more important.
Of course, you can be good at making decisions without actually making good decisions. Your decisions might be crap, and that's not a good thing. Likewise there are many other important qualities that a manager needs to be good at their job, such as putting their team first, finding the right balance between detail and big picture, not trying to build empires, and so on. But you can be all of those things in non-management positions without being able to be a manager. It's decision making, and being comfortable with your decisions, that really separates the managers from the non-managers, regardless of job title.
The good news is that you can learn this, and I really hope you do if it's not already in your tool kit. Manager or staff, leader or follower, you can learn to make a decision and not second-guess yourself constantly afterwards. And once you do, there's no turning back. It's like a ladder that you kick away, and once it's kicked you can't climb back down to be a person who's afraid to make decisions.
Tales of decision-making woe are encouraged in the comments :-)