We will all miss some trading opportunities - due to holidays, sicknesses, errands, personal matters, work, etc - We rarely go over the charts and pick "what-would-have-been" trades. Although we do, thought, go over the trades we did make and see what we did right and what we did wrong. This is what a Trading Journal is for.
The closest thing we do to back testing is when we do simulated trading. This is a necessary part of learning how to trade.  A trader does get used to seeing what the indicators are doing and the best time to enter a trade as well as when to exit a trade. It is a waste of time to do hindsight trading because we were not there when things took place.
If you have been watching live markets for long enough, you'll surely understand how different steady charts are as opposed to live charts. Once you have traded long enough you can see the same moves when you are simulated trading as well as the demo and live trading. We still do simulated trading if we have been away from the market for a few days. This gets us back in tune in just a few minutes, like 15-20 minutes.
It is best to have a rule based system of trading. You might find that when you are doing simulated trading you will make decisions a little different than when you are live or demo trading. This is ok to have some rules that are a little different when simulated trading. The main points here are to be sure and go back to your live trading rules when trading live.
When trading live you will need to use good money management when monitoring your trades. You need to develop good discipline first and prove to yourself that you can respect a clear simple plan. You need to learn how to lose and take losses. You need to learn how to let your winners run as well.
It takes time and patience and many traders won't ever develop that "feeling" because they simply can't detach themselves from their emotions. Be aware that the more trades you take, the more you practice, and the more experience you get. All the above will help you develop experience and a "feeling" for the market. Be sure and read this part twice or three times you must be accountable for all of your trades. There is no system to blame when you take a loss. It's all on yourself and you must learn how to deal with that.
Have fun and relax when trading there is always another day of trading.