When you can not read your own handwriting
As I was a bachelor student we had a professor that discarded the contents of any bottle and flask if it wasn't clearly and correctly labeled. Sometimes we have had spent days and nights to prepare about 1 mg of a sample and it was quite painful to see the result of several days being discarded but that was his no.1 rule that each and every container must be clearly labeled no matter how obvious its content.
Even despite meticulous labeling it is possible that you grab the wrong container and use it. Has it ever happened to you that you wanted to reduce the pH and used a base or vice versa and wondered why the pH doesn't go to the direction that you expect?
In a cosmetic lab you can not cause any real disaster (thanks heaven). Unless you meddle with a concentrated base or acid, there is nothing really dangerous in a cosmetic lab (specially a natural cosmetic lab) but in real laboratories, the slightest mistake can cause explosions and fatal injuries.
This doesn't mean however that you shall not take everything seriously. As serious as if your life depends on that. Use labels and markers that are permanent and that do not fade away or smear easily. To my shame, we have had labels that faded away or completely disappeared upon exposure to heat and moisture. We now have changed those labels and moved to more stable (but less environmental friendly) labels.
My story
Most people use computers and printers in the lab these days or go completely electronic and use only the computer and create and collect all their data in electronic files. Old-fashioned as I am, I love pen and paper and most of the time I prefer to write manually as long as it is possible. This means that I usually write the formulations on a piece of paper and then pass it to my team to prepare the formulation. I then transfer the formulation, procedure and all notices to my lab diary. If you say: "this is not precise and some information may get lost" you are absolutely correct. This is why Swetti, each time before emptying the waste paper bin asks me if I am sure that I have everything transferred and to be honest, it happens several times per month (earlier it was several time per week. You see how I have improved?) that I empty the paper bin on the floor and search in the waste paper for bits of information that I miss. I know this might seem like a waste of time but this is how my brain works (unless I am working remote and in that case I send my team the formulations in an electronic format).
My lab diary is written in 3 languages. Not that I want to show off with my language skills but that's the way I think most of the time. I mean a single sentence is written in 3 languages. This means I start the sentence in German and as I move on I switch to English and Persian or vice versa. This means again, if somebody wants to steal my lab notebooks, he shall send them to a translation office in order to understand what I have written (if they can read my handwriting at the first place). When I go back to the notices later I can sometimes not even read my own handwriting.
Recently I wrote a conditioner formulation and I accidentally read 3% arginine from a previous formulation whereas indeed it was 3% aquaxyl. You see: aquaxyl and arginine have only the beginning "a" in common but I was multi-tasking and didn't realize that 3% arginine is a waaaaaay too much. Even after Swetti asked me if I am sure about 3% arginine I told her that it's correct (again I was multi-tasking). End of the story, the conditioner we made didn't become a conditioner at all. It became something like sour milk and stank to hell.
Well that was a small batch and it was only waste of time and some material and lesson learnt to double and triple check each formulation before we start making it.
May such mistakes never happen in your lab but if, that would be nice to share them with us.
Stay safe and productive