When writing SOPs, detail is very important. Your manager is correct, a random person should be able to complete the procedure. However, the in-depth details should also be concise. A concise and detailed procedure is more efficient that unnecessary words. However, it is also very important to have the document reviewed by as many people as you can. Instruction wrote can be very subjective, the best way to make an objective and concise set of SOPs is to have reviews and take note of peoples questions and concerns. I believe the best way is to write an extremely detailed procedure, then focus on making it concise and follow that by many reviews. The end product should again allow a non-versed person to be able to follow the steps.