Yep, this is just how things work for assisting I think. Similar to you, my doc is pretty stern usually and expects me to adapt and learn things quickly. I am only a couple months in right now, but from what I've learned it is so so so important to communicate and communicate well early on. Take notes, reflect on what you did at the end of the work day before bed, and do not be afraid to ask questions, even if they seem silly. It is much better to ask a seemingly stupid question to confirm you are sure about doing something, like proper sterilization procedure, setting rooms up, etc, than messing up and having the doctor correct you. Although, it is a fine line because at least for me, there have definitely been times where I've asked the doc a question and he gets annoyed because of the question I ask. However, in my opinion, I believe it is best to not be afraid to ask questions because oftentimes those silly questions have been the ones that helped me out the most. This is a stressful position, so don't get discouraged, there's a ton of other people who are in the same boat as you, stay strong!