There are many difficulties and problems with being your own coach. Not being able to see and correct your own movement patterns is one of the biggest. But another huge problem I see among those who don't have another coach is that they tend to let themselves as an athlete influence themselves too much as a programmer.
If a coach has your workouts programmed for you, it very easy to follow them. If you coach writes 7 rounds, you do 7 rounds. No questions asked. But when people program for themselves, they tend to question and change things last minute. If you program 7 rounds for yourself and feel like toast after the first 3, you may start to think: "maybe I should just do 5 today".
It is thoughts and actions like that which destroys your original intentions as a programmer and slows down your progress as an athlete. I have seen this happen on so many occasions to coaches at other boxes, friends, and myself. If you have to be your own coach, you need to be able to separate yourself as a programmer from yourself as an athlete. You need to follow a plan. If something is off in a workout, make note of it and fix it next time you sit down as a coach. Do not make last minute changes as an athlete and let it become a habit.
In other words, when you program, you need to know exactly what the fuck you are planning, as far as energy systems, skill development, and volume, so that you as an athlete can have complete confidence in what you are doing everyday. Everything you will feel, every discomfort that will pop up, and every mentally tough portion of a workout should be known, calculated, and if possible, visually prepared for. There should never be any "wow, this took longer/shorter than I thought" or "that was a lot harder/easier than it looked". Surprises are a sign of a novice.
The easiest and best way to avoid this major problem is to find yourself a good coach who understands and has reasons for everything they have you do. Every athlete should have a coach. There are almost no great athletes out there who are not under the direction of at least 1 coach.
If you cannot find a coach, do the best you can. Ask lots of questions, track lots of data, and prepare to make lots of mistakes. And most of all, do not let yourself as an athlete influence yourself too much as a coach.