A simple (?) question about basic stock trading.

Hi,

So here it is, something I always wondered about;

Will there always be enough sellers/buyers available when you want to buy or sell?

Of course Hollywood always makes it look simple and easy; buy low sell high.

But will situations arise where there just aren't enough available stocks going around.

I can see situations where a lot of people are buying when stocks are at an all time low and selling when they are insanely high (the stock, although the people might also be ;-), there must be times when supply and demand aren't in balance.

It sounds easy, selling when the stocks are high, but what if not enough buyers are interested at that moment? The stock price would be ideal to sell, but you just can't. What if the stock prices plummet shortly after, would you have missed out because you couldn't sell?