You don't buy coins blindly because it is cheap so you don't get trap. Many projects are dead on arrival and so when you invest, you go down with it . You need proper research before investing on any project.
I agree in what you have said because not all coins in the market is worth to buy and invest. Even a coin is in a dip, you should always do some research and study the market movement of these coins. Don't waste your capital in many worthless coins instead invest wisely.
Actually as long as the market cap is healthy there is no reason to worry, you can easily manifest which coin is going to be abandoned or if it cannot recover from a dip, usually I use market cap as an indicator of whether the coin is still worth to buy or not. Yes research is important as well but there are really good coins with good background that fell off and did not recover.