Currently; the prices of coins are not in good condition to invest. Most of the coins are bearish now. It is hoped that at the end of this year the market will be able to get it's bull back on track.
Who told you, this is not the best time to invest. This is absolutely the best time to buy the potential coin at the very cheap rate. Good investors are the market loading their bags with more cryptocurrency. Buy and HODL for a better ROI.
As for the current condition of coin price and sustainability of cryptocurrencies. There is not cause for alarm right now as everything that is still happening is just market correction. We cannot experience that kind of bull run of late last year without a proper market correction but i can assure you it is almost over. we are getting closer to our next bull run.