On any given day the stock market will go up some and down some. Long-term investors in publicly traded businesses should focus on things such as growth in revenue, net income and free cash flow and whether or not they sit behind high barriers to entry.
Remember there is always a risk of permanent loss in the stock market. The most widely known route to a permanent loss is bankruptcy. Another way is that a company that you own shares in may go private at a price less than what you paid for.
In a day and age where employment is increasingly tenuous, it pays to maintain the viewpoint of building your own security. People needs to build their own retirement, healthcare and (increasingly) even their own career by owning a business or pursuing some form of self-employment as employers increasingly become unreliable. All of this takes money. Save all you can while you can.