Utilize your financial knowledge, give your answer or opinion to the input question or subject . Answer format is not limited.

why would someone buy or sell just a few shares in stocks 
Simple, there is no magic price adjustment after sales - why do you expect the stock price to change? The listed price of a stock is what someone was willing to pay for it in the last deal that was concluded. If any amount of stock changes ownership, this might have the effect that other people are willing to buy it for a higher price - or not. It is solely in the next buyer's decision what he is willing to pay. Example: if you think Apple stocks are worth 500$ a piece, and I buy a million of them, you might still think they are worth 500$. Or you might see this as a reason that they are worth 505$ now.