Microsoft announced Tuesday that it’s buying Nokia’s mobile phone business for $7.2 billion. Back in 2000, when the Finnish company was the top mobile phone maker in the world, its market value peaked at about $300 billion.

Around that same time - before launching the iPhone - Apple was worth less than $10 billion. Now its stock is valued at about $450 billion.

That’s quite a reversal of fortunes for both companies, wouldn’t you say?

Competitive markets are just like that. One day you’re fighting bankruptcy and the next, you’re sitting on $120 billion in cash. On the flip side, I’m not sure any position is more tenuous than when you’re on top of the heap: every competitor has a bulls-eye painted on your logo and the only way to go is down.

It’s the same with careers. Whether you have one or multiple peaks, nearly all of us eventually decline. Few get to exit while they’re on top. Yes, I know that sounds like a morbid topic. Why even go there? Because you’re probably not aware of which side of the slope you’re on and it’s very, very important to know.

Let’s say, for example, that you’re a mid-level manager trying to break into the executive ranks. If you’re still on your way up, you can invest in your future. You can take relatively big financial and career risks without fear of getting caught with your pants down.

But what if your career star has risen about as high as it can go? What if you’ve already peaked? Then you’re going to have to manage your career and your finances very differently. You’re going to have to be far more conservative and risk averse.

The same is true of wealthy, successful executives and business leaders who continue to live high on the hog long after their sun has begun to set. They’re either unaware or in denial of their actual situation. Next thing they know, it’s margin call and they don’t have the cash.

That can happen to anyone. It actually does, all the time. To avoid that fate, here are a few things to keep in mind. At a minimum, it’s good, sound advice. But if it feels like I threw a brick at your head, that’s a sign that you should really pay attention and listen up before it’s too late.

There’s no standard model for this sort of thing. Trust your internal compass.

Some peak in their 30s; others continue to go strong well into their 60s and beyond. Look at Betty White. I think she’s like 91 and still costarring in a sitcom, Hot in Cleveland.

If a realtor says you should buy a house based on your future income, you may want to corroborate that advice with your own internal compass. Speaking of which, that compass should have both logical and emotional components. In other words, use cold hard reasoning but also trust your instincts. If they conflict, I’d go with your gut.

Sorry to pick on realtors, but the same is true of financial advisors, coaches, anyone who might benefit from the advice they’re giving you. I’d take it with a big old grain of salt. Instead, listen to the advice of people you trust, but always make the final call yourself.

Hope is a lousy strategy. Get real.

People who are so self-aware, so grounded in reality that they know exactly where they are on their career curve are few and far between. Trust me on that. Besides, there is such a thing as luck and some things are simply beyond your control. Don’t hang your plan on hope. It’s a bad idea.

I know they say “hope for the best and plan for the worst.” I’m actually not a big fan of that model. Instead, I would prefer you get as close to reality as you can. Sure, you can have hopes and dreams until the day they pry that MacBook out of your cold dead hands. Just don’t assume your dreams will come true.

And, in spite of what I said above - that you can’t count on age as a guage - the later in the game, the more important it is to know the truth about where you stand. In other words, you probably can and should take more and bigger risks when you’re young. Further down the line, you might want to take an internal career audit a little more seriously.