"No mattress building allowed."
That's what a piano student of mine, who also happens to run a large factory, tells his staff when they begin a report say saying "Well, we didn't really have much time to prepare this" or "I'm not sure if this is any good or not."
He's not being critical of their work, and in fact, he's very encouraging to his coworkers. What he's telling them is: "Don't put down a comfy mattress to catch you if you fall." "Just do your best and let your work speak for itself." And, if it's not perfect, keep refining it until you're satisfied with the result.
This is good advice, and we heqr this kind of "mattress building" all the time. A man walks up to the podium and begins his speech with "I'm not too good at public speaking..." Or a woman makes an awkward joke about her height as she lowers the microphone. (I've seen this one several times!)
We pianists often do it as well. We sit down to play our favorite song for our friends and say, "I haven't practiced this as much as I should have" or something similar.
In most cases, this type of mattress building works against us, and against our listeners as well. It takes us away from what we really want to say, whether verbally or through our music, and it tells our listeners, "You probably won't enjoy this because I'm not that good."
My friend is giving good advice here: Don't build mattresses.
And here's the most important point: You don't have to.