When the Dow Jones Industrial Average crossed 15,000, it had me dreaming of bigger things.

Specifically: Dow 116,200.

That was the market level predicted by mutual fund pioneer Bill Berger in a 1995 speech at a Society of American Business Editors and Writers conference in Boston, and it was almost as laughable then — with the Dow at 4,500 — as it seems now, when it stands more than 100,000 points into the Dow’s future.

Berger wasn’t expecting hyperinflation on the index; instead, the 70-something founder of the Berger Funds (which shuttered shortly after his death a few years later) said the market would reach his magic number in 2040. He wryly suggested that if he was proved wrong, people should visit him in the 2040s to discuss it.

Yet with the Dow at 15,000, it doesn’t really look like Berger will be off by much, as far-fetched as it seems.

I look back on Berger’s prediction periodically because he could not have foreseen the events that have happened since. In fact, that was a huge part of the point he was making at the time, about the difficulty of forecasting.

In 1995, the market was about to catch fire, and Berger didn’t live long enough to see the Internet bubble burst. He was not predicting the horrendous 2000s and, in fact, his point in looking out so far was that he didn’t feel that interim events — even catastrophic ones like the financial crisis of 2008 — would make much of a difference on what the market would do in the very long term.

It’s a lesson worth revisiting at a time when many investors are worried that the market cannot maintain its current highs, let alone proceed on any pace that would make 116,200 ever be a reality.

Traders work on the floor of The New York Stock Exchange on March 5, 2013. Getty Images

The basis for Berger’s forecast was simple. By 1995, he’d been in the investment business for 45 years, and had seen the Dow go from below 200 to just over 4,300. Mathematically, Berger saw the Dow’s future as reflecting what had happened in the past, thus moving it from 1995 levels to 116,200 in 45 years.

Using easy, round numbers, the Dow needed roughly 16.5 years to triple from the time of Berger’s prediction, crossing 13,000 early in 2012.

Using the Rule of 115 — a rough measure of how long it takes for something to triple based on a constant return — that’s a gain of roughly 7% per year.

If that rate of return holds for the future — and it’s smack in the middle of the 6% to 8% long-term range that many market observers believe is realistic — then the Dow would triple twice more over the next 32 years.

If that happens, the Dow will cross 116,200 sometime in 2045, a bit after Berger’s time frame but not wildly off base, especially when considering that the forecast would have made investors break out in hysterics had it been made, say, any time after 2000.

Plenty of market watchers will tell you that we are living in changing times, that the 45 years covered by Berger’s forecast are radically different than the ones included in his investing career.

That actually would play to his point, which essentially is “markets go up over time; hold them long enough and you’ll be rewarded more than by following any forecast of what is likely to happen next.”

Investors want to attach significance to market milestones, but a new level for the stock market is more like crossing a state-line than breaking the sound barrier. It signals that a new territory is being entered; it doesn’t change the game.

Meaningful or not, investors typically react to landmarks by:

A) Seeing it as a warning that the market is getting too high, so that they back off or go into wait-and-see mode to determine if the market is resisting the new highs.

B) Viewing it as a sign of things to come, so they jump on board to make sure they don’t miss out on the index’s next benchmark.

C) Treating it like any other number, having no more impact on what happens next than yesterday’s box scores have on games scheduled for tomorrow.

While short-term moves can pay off, the real question is whether they jeopardize long-term strategy. It’s more important to capture the market’s performance over a lifetime, rather than a week, month or year.

There have been times since Berger’s forecast — such as the Internet bubble days as the Dow barreled towards 10,000 — when his prediction seemed way too low, and other times — like the two bear markets in the 2000s — when it looked way too lofty.

Of course, during those periods, the market was volatile, but its move was not sustainable indefinitely.

While it feels great to load up when the market is running and avoid the pain when it is lagging, the average investor needs to recognize that their mission is to capture the trend over their lifetime, whether the Dow is at 5,000, 15,000 or anywhere up to and beyond 116,200.

What Berger said in 1995 holds true today: “There’s not an investor who has been alive for the last 60 years or more who hasn’t seen the market rise over their lifetimes.” That period included a chunk of the Great Depression.

“So I don’t know exactly where the market is going over the next five or six decades,” Berger said, “but I know it will be up.”

That’s about as much as any investor should read into a market milestone. Berger noted that market milestones tend to bring out the forecasters and prognosticators, and he cited what he called “the two rules of forecasting.”

Rule 1: For each forecast, there is an equal and opposite forecast.

Rule 2: Both of them are wrong.

Keep that in mind as you consider Dow 15,000 and you hear the market-watchers and soothsayers tell you what they feel is about to happen. If you must find peace of mind in a forecast, find one that takes a long view over a significant, meaningful time period.

There’s a decent chance the Dow hits 116,200 before 2050; it may even do it on Berger’s time frame of 2040. About the only thing investors should count on, however, is that the journey from here to there will be long, bumpy and difficult to make.