I think if you invest in a coin that has a high volume and of course has a product, then you don't need to worry about the money you invest even though the price of coin is down, because I believe the price of coin will definitely increase very high if the project of coin has a product that will be useful in the future and of course the project has progress.
That is true, we not lose anything if we are invest on top 100 coin based on CMC and hold it until the price going up again. My asset drop 90% after buying coin on late 2017. I hold my coin and i belive if bitcoin start to hit $19.000 again, and altseason is coming, my coin will be back to price i bought. Another option is, cut lost and buy back if need it.