Never sell a bitcoin for USD!! SPEND IT on things or service or commodities.
+1000 I've never understood the logic in selling bitcoins.
The logic resides in the fact that fiat currency is still very stable for the most part. Bitcoin hasn't been over the years. When it comes to finances people want some stability. If they can make some money through a bitcoin investment or they can cashout to prevent losing their entire investment you will have a hard time convincing people not to.
That isn't logic, it's normalcy bias. Use bitcoins to buy things when you need to buy things, but for goodness sake don't trade it for an inferior form of money. I fear that too many people new to bitcoin don't understand this simple concept and they're selling bitcoin out of fear that it might trade lower...or they want to lock in some gains. Some people say that bitcoin can't go up in value forever...but in fact it can. In fact, it's designed to go up in value forever over any sufficiently long timeframe so long as it's the best form of money in existence (which it is and will likely forever be).