How this speech pattern works is twofold:
First, any kind of hedging (it seems to me, I think, it appears that lately) is literally a less extreme position than the same sentence without it. Compare:
Your work does not meet our standards
I am worried that lately there have been some days when your work has fallen just a tiny bit short of our standards
That's not a "psychological trick" it's actually a lesser claim than the undecorated statement, which most people hear as:
I am completely sure that every day, always, your work is significantly short of our standards
So because the complaint or negative feedback is being diluted and made milder, people don't react as strongly to it. I am not saying you are 0 out of 10, just that you're sometimes 8/10 and I need you at 9/10 all the time.
Second, the longer and more convoluted wordings give the person more possible "compliant" responses as well as more possible responses. The blunt statement is really hard to respond to. What can you say besides "sorry" or "yes it does meet your standards!" But to the longer statement you could say:
- I agree, I have had some bad days, I will make sure that doesn't happen again
- Please, do not worry, I am also aware of these bad days and am working to prevent them
- Yes, I am a little below par but pretty close to it even on my worst days, and remember some days are still well above par
- I actually think those standards are unrealistic and that most of the department falls below them occasionally
And so on.
If you have negative feedback to deliver, you need to sit with it for a while yourself and understand what you are trying to communicate. If it is "you are not good at this job, you fail every day, we have started the process of firing you and I am taking you aside to do you the favour of letting you start looking for work now instead of the day you're fired" then you don't want to do any of this hedging and diluting. But if it is "last Thursday you were less successful than you should be, you need more days like Friday" then that is what you say. Not "your work on Thursday was unacceptable." That statement is broad and comprehensive, doesn't contain much a person can act on, and is more upsetting than a more diluted and accurate statement.
This is even more important in written communication. In person, a friendly tone, a smile, body language and so on can all soften a blunt statement like "that report was simply unusable." In writing, work hard on being precise, on not overstating the failure, and of focusing on what you expect to be done about it rather than only registering that something was not ok. Perhaps
that report was incomplete (you did not include the Europe data, there were no references), hard to understand (a few graphs would have helped enormously) and needed a copy edit for the numerous spelling and grammar errors. It did not use our report template and you omitted the meta data all reports must contain. I have asked [someone] to redo it.
If you're not that confident, the graph thing is more of an opinion, there were just a few grammar errors etc, you would dilute this list accordingly. So "I think the European data is important to have included" for example.
Then you can ask if the person needs training, if there were issues with this particular assignment, or other things that try to solve the problem. Or if they've done tons of great reports before,
Your previous reports showed none of these deficiencies. I'm going to continue assigning this kind of work to you and look forward to a report that meets our standards for your next assignment.
Just please don't do the "praise sandwich" where you tell them they are usually great, this time they were terrible, and you're sure they'll be great again. Studies have shown that the minute the "terrible" part stops, the listener decides you didn't mean the praise part. It's awful. Just tell them they were wrong, but don't come across more extreme than you actually mean.