A lot has changed in the past year in the stock market as growth stocks have been crashing hard, with the Nasdaq dropping by 15%. Even the more stable S&P 500 has fallen 6%. Concerns about inflation and a possible recession are weighing on investors.

But despite these fears, many investors are still making potentially costly mistakes by focusing on current trends and hopping on stocks that simply aren't good buys. Here's what I mean.

Investors are taking on too much risk

Billionaire investors Warren Buffett and Charlie Munger have compared the markets to a gambling parlor. This could explain why a struggling retailer like Bed Bath & Beyond, which has incurred losses of more than $866 million over the trailing 12 months, can skyrocket more than 45% within a single trading session as it did last week.

Another example of that gambler mentality is the desire to invest in companies that have monkeypox treatments or vaccines. Shares of SIGA Technologies, which makes a monkeypox treatment, have jumped close to 260% in just the past six months. Bavarian Nordic is up 64% during that period as investors are hopeful about its monkeypox vaccine. Meanwhile, the S&P 500 has declined 4% over that stretch.

While some investors are earning quick profits on this short-term trading, buying at the wrong time could lead to significant losses. There's also the danger of hanging on too long with these types of stocks.

What's hot today could be a dud next year

If you end up buying a stock based on a short-term trend, the risk is that when the frenzy calms down, you could be left holding the bag, with an investment that doesn't look nearly as exciting as it once did.

COVID-19 vaccine maker Moderna (MRNA -1.04%) is a good example. Last year, its stock price jumped 143% as rising COVID case numbers made the healthcare stock a hot buy. This year, the company expects to generate $21 billion in revenue from its vaccine.

But beyond that, there are big question marks surrounding the business. Moderna's focus on COVID has resulted in a lack of diversification for the company, and that has made investors wary of the stock. It's down 40% year to date.

It's a similar story for rival COVID vaccine maker Novavax, which in 2020 jumped by a whopping 2,700%. But with its COVID vaccine not obtaining Emergency Use Authorization until just last month and the company slashing its sales forecast for 2022 in half, its shares are down 75% this year.

Investors shouldn't overlook fundamentals

The key takeaway for investors is to focus on long-term trends and a company's business prospects beyond just the short term. While SIGA Technologies might be a hot buy this year, it could give back many of its gains if monkeypox cases subside and the disease doesn't derail the global economy the way COVID has over the past few years.

More stable healthcare stocks, such as Merck and AbbVie, have proved to be sound investments and have outperformed the markets this year, with returns of 19% and 4%, respectively. Although they might not generate sky-high returns in the short term, they also won't jeopardize your savings and put your portfolio at great risk.