A common mistake I've seen people make, and I've made a lot myself --
Thinking others will give the same care to your affairs that you would to theirs. It doesn't happen.
There's a quote from the Talmud, it's one of my favorite quotes and I think one of the most important:
"We do not see the world as it is. We see the world as we are."
On the surface, it's a simple quote. The optimists see the opportunities and the pessimists see the barriers.
But it also applies to things like integrity, people keep their word, carefulness, diligence, etc.
I've seen a lot of talented and focused people, time and time again, be disappointed in the results they get from other people.
Other people are actually perfectly reliable, as long as you've got the correct expectations and you structure things correctly. It's only when you start to expect unrealistic things and structure things poorly, that things don't work out well for you.
So bear this in mind next time you're delegating something to an employee, staff member, or even a skilled professional like an attorney, accountant, or doctor -- don't project your values and work ethic onto them.
A few people -- very few -- will do better work for others than they do for themselves and in their own life. To some extent this is cultural: Japanese people are more likely to act this way. It also relates to pride in work: people who see themselves as master craftsmen and love their craft are more likely to act this way. And some people have a particular honor code about it.
These are fantastic people to work with, and ought to be looked for. But even then, the assumption should be that a person will handle your affairs as well as they handle their own at best, and oftentimes slightly worse. So bear that in mind -- if you're focused and diligent, make sure to bring realistic measured expectations to table, and then you'll never be disappointed.