The more the market capitalization of a coin, the lesser the market manipulation of the coin.
Let us take bitcoin as an example, owned by many people in the world and also having a market capitalization of over $500 billion now. To manipulate a coin like that, I mean to manipulate a coin like bitcoin, it would be difficult.
A coin that is just listed on exchanges, or that is control mostly by whales, like 40 to 70% or more controlled by whales. Such coins can be manipulated. That is why it is good to go for good coins like bitcoin that is difficult to manipulate.
but after all they also predict by trend lines and indicators? why trend lines matters?
Indicators and other things used for technical analysis are good because traders use them and they have better accuracy. This does not mean that you should 100% believe on indicators because they can also fail, although many professional traders are using them and showing satisfying results.