Which one do you want?
Imagine you are visiting a doctor for your ECG.
You have the following 2 choices.
I am confident that each and every one person would want the one moving up and down. This means that you are alive.
The straight line means DEAD.
Likewise, when the stock markets go up and down, it means the markets are ALIVE. A straight flat line means a DEAD stock market.
This is for representational purposes to explain a concept through visual means.
Which one would you prefer? As always, the choice is yours.