Perhaps you accidentally set some kind of setting or something similar, to your coin sold automatically. Because it couldn't just happen. You're right, we should check our coins more often.
If you are not really familiar with this business better to keep watching the market and see if you can take some advantage, it's not luck but your skills
to developed when you are trying to work out with this industry, you can keep making good decisions when you have good knowledge about this business.
There is no luck factor involved in the crypto trading because all are technicalities here once a trader is capable enough to understand and getting through these technicalities then there is no loss. All the knowledge she keeps will help us in preventing from bad decisions and to grab the good ones. Still if you have learnt a lot and not working well then you should start from Altcoins practice it well and upgrade then.