This is a basic question. No matter how low the current price, will my stock position sell? Please see my explanation.

I understand that the idea is to buy low and sell high. What if I own some stocks that are low, lower than I bought them for over a year ago. If I call my broker and tell him to sell, then he clicks his sell button. Here’s my question: will there always be a buyer or bot somewhere that will ALWAYS buy this stock, automatically and instantaneously, no matter how low it’s selling for? And, in this case, basis cost – sell price = capital loss? (Not including any commission fees, etc.). Thank you