Welcome to fickle and ADHD altcoin markets. Even if a coin has significant merit it's not prudent to simply hodl.
Sometimes you won't be able to point to a specific reason a coins 'irrationally' tanking unless the rise up was just as irrational.

I argued about the overvaluation of MRO a few weeks ago:

https://bitcointalk.org/index.php?topic=578192.msg6572921#msg6572921
https://bitcointalk.org/index.php?topic=578192.msg6573363#msg6573363
https://bitcointalk.org/index.php?topic=578192.msg6574031#msg6574031

I didn't buy at that time because the price was pumped too high-  which most argued against. People think this is a naive argument which it is but doesn't stop it from being true.

I waited few days for price to fall by more than 100% to buy then sold at around 590-620% profit, Not the best but perfectly comfortable with that. I'm not buying back at this time.

Many people have not factored in the final supply nor consistent inflation because they don't hold the coins in a long term purview. Emission curve means nothing to many when they are trading on daily or weekly intervals and moving onto the next coin, even if it's a shitcoin the smallest gimmick or development can allow a near guaranteed profit. You can't really go against the grain of the market when you working on short to mid term. no reason to stay in one place when there's consistent % gains denominated in BTC to be had across the whole market.