Mixing hope with experiences

A friend and I spoke the other week about the problem with hope and experiences. You have this hope about people and situations, then you have your previous experiences that add into the situations. The notion that "previous behaviour is a prediction for future behaviour" and at the same time "giving people the benefit of the doubt and believe in them". We discussed in work context, they admitted to feeling naive since their approach to coworkers was that people
a) want to do a good job
b) care about the job
c) are telling the truth

However, what they have found out with experience is that a lot of people they work with seem to mainly be there in order to get a pay check and - this was the main cause of concern and annoyance - cover up and "looking good" while not doing anything. This was especially exampled in "they offered to help out, took over the task since I was busy, but ended up doing nothing and now I want to take the task back but it will cause a ruckus". I recognize the last example, I've encountered it myself and it is a little tricky to keep the environment happy without sounding like you are "selling out the person to your boss or others" and not getting thrown under the bus yourself.

The idea of "having hope" or "giving people a chance" (or two or three) has severely been challenged by my experiences that keep growing. I'm not saying I'm not giving people a chance anymore, I do. I probably give them too many*. However, it's part of the "using experience instead of only hope" that makes you to make alternative plans, make check points (things can get saved if you have early check points instead of waiting until deadline to confirm work), and most of all - getting used to the idea that "someone else's job is not your responsibility to fix great but to be there and help if they need help" and if that doesn't happen, well... it just doesn't. I should really work on how to phrase it since I'm sure it will be interpreted wrong.

What I mean is this, and this goes for things that aren't yours - not the things you delegate, that's slightly different.
a) if it isn't your job, don't fret too much about it since someone else is responsible and hopefully they have their ducks in a row (even if it might not be in your kind of row)
b) if you are working in a team, see if you can make clear to have check points/team meetings where reports are given so you all can make sure everyone is working on schedule
c) don't take over someone else's job just because you can do it better, do it faster, or do it "right" and IF you end up doing someone else's job - it has to be noted somewhere (preferably your boss) since otherwise you are on a track to end up as "the responsible cleaner" and risk missing doing your job as good as you can (and this will end up being bad for you).

Responsible cleaner = the person whom everyone knows will do a good job and fix problems for others, in short time frames (even when it means their own job will lack), and additionally some times without telling the boss thus making it less clear that someone wasn't doing their job.

It's important to understand a distinction here; It's not about telling on someone, but making sure your work doesn't get hurt in the end. Because I can tell you, when it comes to your job performance review it's going to be about how well you performed the things you were tasked to do, not others' tasks that you cleaned up. Sometimes it can be changed of course, if priorities in a group has shifted. In my experience though, I can't say that this really shines through as much as "why haven't you performed this thing" (especially if the 'cleaning up' happened more than a month from review time, people have short memories).

I guess what I'm trying to say here is: keep the hope to maximize your chances of success if it turns out that hope was slightly misgiven. That's what my experience tells me anyway.

*let's not go into personal compared to work... that's even harder