It's ugly out there. The S&P 500 (^GSPC -0.60%) is 25% below its January peak, and after its latest rout sits within sight of new multi-month lows. Yikes! Whether you're a new investor or a veteran, it's tough to feel confident about putting money into the market right now.

If you truly believe in a long-term approach, though, this could be the time to do exactly that. Just buckle up if you're going to take the ride.

Not quite but close enough?

The market could still easily move lower before moving higher again. The average bear market drags the S&P 500 to 36% below its peak, according to data from mutual fund company Hartford Funds, while brokerage firm Edward Jones calculates the average bear market lasts about 15 months. We're not quite at either mark yet.

^SPX Chart

Data by YCharts.

Trying to step in at the precise end of a bear market and the very beginning of a new bull market, however, can prove costly for a couple of different (but related) reasons.

The first reason: You're not going to be able to identify the bottom while the bottom is being established.

Plenty of pundits will argue with that, claiming the market gives clear hints it's hitting bottom. And there might be something to their arguments -- the stock market may be somewhat mechanical some of the time. But those hints are not consistent enough to count on when you're making major buying and selling decisions. At best, it's an exercise in futility; at worst, it's a way of talking yourself out of a great opportunity at the worst possible time.

Why? Consider the second reason you should be more inclined to invest right now despite the clear bearishness rather than hold off: Not being in the market for the entirety of any bullish reversal can cost you ... a lot.

Edward Jones had some curious findings regarding recoveries. Chief among them: The five most recent bull markets averaged a gain of 25% in just the first three months. That's a sizable chunk of the average total bull market gain (more than 150% from beginning to end).

Or think about it like this: While this bear market isn't 15 months old and hasn't reduced the S&P 500's value by 36%, it's closer to both of those milestones than not.

The real danger

Whether or not it's safe to step into the S&P 500 now that it's 25% below its peak mostly depends on your personal situation.

If you're going to need the capital in the very near future (say, for college tuition or to buy a home), then there's danger in being exposed to stocks here. If you're nearing retirement, that also complicates the answer.

Impending retirement doesn't necessarily mean you should remain on the sidelines. While you may start withdrawing some of your retirement funds right away, for most investors the bulk of any retirement savings won't be tapped for years down the road. It would be nice to grow that piece of your nest egg in the meantime, and stocks are still the best long-term growth engine around.

Perhaps a better question to ask is this: Are you more afraid of losing money in the short run, or more afraid of missing out on an opportunity to make money in the long run? If your portfolio reflects an outlook of five years or longer, your bigger danger isn't being in the market when things are a little rough -- it's not being in the market once things finally take a turn for the better.

Most investors fear the former until they've had a chance to consider the consequences of the latter.