I have always believed there are an infinite number of mistakes to be made in weaving. I also believe there is no mistake you cannot fix (if you will take the time). Plus, there is something I like to call "The Fudge Factor". Simply defined, some "mistakes" you can fudge and some you just can't. The trick is knowing which you can fudge and which have to be laboriously repaired.
After 50 years of weaving, I just made a mistake I have NEVER made before! I was so stunned I laughed. This is what I did. I don't know why I decided to begin sleying the reed in the first dent, but I did. Once I was through the reed and had adjusted the tension, I went to add the floating selvedge only to discover I forgotten to leave a couple of extra dents. (duh)
Do I completely un-thread and move the whole 36" warp to the left 2 dents? I don't think so! Employing the Fudge Factor, I pulled out 4 warp ends causing the borders widths to not quite match.
Below is a mistake I make far too often. I forget to center the metal rod I tie the warp onto. Then as I weave, it sticks out too far on one side to advance as I weave. I was lucky this time. I had just enough clearance, so I didn't have to re-tie the warp.
This always happens to me. I pull in a little bit in those first couple of inches before I even out. I used to go crazy about this, but I finally discovered, it really doesn't make enough of a difference for me to try to make it any better. It is true that when you take the finished baby blanket and line up both edges---there is a one inch difference.
I usually don't talk about the fudge factor and how much I use it in every step of my weaving. (and in every weaving)
I have weavers complement me all the time on how perfect my weaving is. If you only knew, oops, now you do (grin)
Mistakes I always fix:
Threading errors in heddles and reed.
Knots in warp
A missed pick
Warps I will cut off the loom: (I haven't had to do that for many years now, but I can tell you that I have done it more than twice.)
Warp threads that break every inch of weaving. (I can take about a foot of that!)
Warp threads that stick so I can't make a shed.
Mixed warp threads that have different tensions.