You are correct that beginners cant understand their mistakes, most of them. So good basics are key in building a foundation. Keeping a journal. Log every trade. Spot the reason for wins and losses. Recognize the fact that there will be losers. As long as the process is followed, the statistics can be collected and from that, the strategy being used can be validated. A well defined strategy helps reduce emotional decision making, maintain discipline and create consistency. There are online tools that help with that.
And a strategy is a systematic approach to trading, and most of it is catered to a certain market condition. When using it, a certain set of tools is needed. Say for example, trend following. The indicators used for this strategy will not be suitable for trading S&R. If only one strategy is mastered. Then you can only hope to trade a certain market condition successfully. The common solution is universal strategy, But then again, you need to be able to recognize the market condition, have the required indicators to assist in trading it. No single strategy works for all conditions. So if one single strategy is mastered, you will only specialize in that specific market condition or you can learn and maintain a multiple approach in your arsenal.
Imagine trading is treasure chest. that requires a key. Only you can find the key to unlock it. Gaining knowledge, knowing yourself, know the market.
Trade safe.