That's what it felt like when I did my PhD. I was only until about half way through that I sort of knew which way was up an which was down. By the end of my PhD I felt I knew enough that I could have started my PhD project. The entire experience was a mixture of panic, feel of incompetence, resentment...

Not sure who to feel angry at, myself for choosing a PhD project when I knew fuck all about the fundamental technologies underpinning it, or my supervisors for not providing me with more pedagogy on those technologies. Sure they helped a lot when it came to writing papers, giving presentations, devising experiments etc. but they spent practically zero time just sitting me down to teach me the essential fundamentals instead of leaving me blind.

Oh well, I learned an important lesson to not start a job I'm not qualified for.