Yeah your right its unpredictable but its depends of your strategy and what altcoin you choose..
In my opinion or tips i think better to always use coinmarketcap and choose top 20 altcoin or top 10 altcoin and choose them because those are legit altcoin that you can hold for a long time.
Though you have very good strategy and have choosen a good altcoin, but you can not always beat the market.
The market is always right. So i can say trading is unpredictable but good strategy and good choose of altcoin can reduce the risk of unpredictable.