Why technical analysis is not reliable

technical analysis is a useful tool for traders, but we have to consider it’s limitations. Technical analysis is basically based on assumption about the past market statistics and data, without putting into consideration other external factors . So traders should not 100 percent rely on technical analysis, they should use it together with other methods of analysis.
Some of its limitations includes
1.it is based on assumptions about past market trends, gotten from the past market price and  volume data
2.it is a backward tool subject to interpretation from different traders.
3.Technical analysis will not provide the full details of the market,  that is putting economic and global events into consideration,
so traders should put all these factors into consideration before making an investment decisions using technical analysis.