After months of bear market blues, investors found something to cheer about in recent days: The S&P 500 finished last week 20% higher than its October low. And that's prompted many to call a bull market.

These times of market growth always follow bear markets. So, we knew a bull market was coming. But the big question was, when?

And that question may still remain. Morgan Stanley's chief investment officer Mike Wilson wrote in a Monday note that "the bear is still alive." And he said investors should expect more declines. Meanwhile, it's important to note that the start of a bull market generally involves the benchmark reaching a new record high -- and we're not there yet.

Considering all of this, should you invest right now? Let's find out.

A potential 14% decline

First, a closer look at Wilson's predictions: He expects the S&P 500 to fall about 3% in the coming 12 months, Fortune reported, citing the strategist's note. But his bear scenario calls for a 14% drop from current levels.

The reason behind a potential decline? Wilson says Wall Street's forecasts for profits are too high considering the current economic climate, according to the newspaper. The forward earnings expectations for 70% of S&P 500 industries are "at least 20% above pre-COVID levels," Wilson wrote. He expects declining inflation to weigh on corporate profits -- and that should limit the performance of stocks.

The investment chief likened today's situation to the period following World War II, Fortune reported. After the war, a bear market rally eventually led to new lows. Investors flocked to the market to participate in the rally, only to see stocks fall farther a short time later. This involved a period of rising interest rates and a recession. 

And as mentioned, the S&P 500 still hasn't reached a new record high. Generally, both that and a 20% gain from the previous bear market low are required to call a bull market.

All of this means we probably shouldn't be so quick to call recent gains the start of a bull market.

Now let's get to the big question: Should you invest?

Bear market opportunities

The short answer is "yes." Here's why: Long-term investors can find opportunities in any market -- bear or bull.

Bear markets, in particular, often offer us a chance to get in on quality stocks trading for a bargain. These players may be struggling a bit during the tough times, with headwinds like higher inflation, for example. But they have the strength to perform over the long haul.

An example of this is Etsy (ETSY 0.34%). The e-commerce platform for handmade goods kept the growth it gained in the earlier stages of the pandemic, and it remains profitable. But today, declines in the share price have left it trading for 21 times forward earnings estimates -- a steal considering long-term prospects.

With Wilson's prediction of more market declines, though, you may be wondering: Why should I buy now if I can scoop up shares cheaper in a few months? The thing is, it's impossible to time the market. You may be able to buy the shares cheaper down the road, but there's no guarantee.

Let's take a look at Amazon's (AMZN 3.43%) performance this year. It's climbed about 50%. And that increase began even as economic headwinds continued to hurt earnings. This means it's impossible to guess exactly when stock performance will take off.

The best strategy is to invest in quality companies when their valuations look reasonable -- in a bull or bear market. If they extend declines after you buy, that's OK. It's unlikely this will make a big difference in your overall return if you hold on for the long term.

Finally, even considering Wilson's prediction, there's reason to be optimistic about investing today. As mentioned, declines in the market offer us opportunities to get in on or reinforce positions in quality companies that are likely to perform well over time. And even if the bear market isn't over, the next bull market may not be far off.