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Some great investment returns just sneak up on you. That stock you're watching seems primed for nothing special, or maybe a downright disaster. Then the chart squiggles suddenly skyrocket, rewarding shareholders with massive returns.

And you missed it.

Here at the end of 2016, that's how I feel about longtime graphics-chip rivals Advanced Micro Devices (NASDAQ:AMD) and NVIDIA (NASDAQ:NVDA). Their stock charts took a drastic positive turn this year, leaving me flat-footed alongside many other investors.

And you know what? I kind of wish I had added to my Netflix (NASDAQ:NFLX) stake in early February, or perhaps the middle of the summer. But I didn't. So here I am, telling you all about those missed opportunities instead.

The sudden graphics-chip turnarounds

Let's be honest -- nobody, but nobody, had any real reason to believe that NVIDIA or AMD would soar sky-high in 2016.

Both companies were polishing up brand-new architectures for their graphics chips, and AMD was also preparing to launch a new platform for PC and server processors. That might sound promising at first glance, but both companies have a history of fumbling important technology launches.

NVIDIA and AMD shares were already on a roll, as investors were hoping for the best out of those important chip announcements. As New Year's rolled around, the stocks had gained more than 60% in just five months. That could very well have been the end of this story, setting investors up for huge corrections if anything went wrong.

But both AMD and NVIDIA reached into their top hats to produce some good-looking bunny rabbits. They proceeded to unveil the new NVIDIA Pascal and AMD Polaris chips, selling truckloads of these products in the second half of the year. AMD delivered three earnings surprises in 2016 along with strong top-line results, and NVIDIA blew every target out of the water.

I did not see any of this coming, and can only glare ruefully at their year-to-date returns. NVIDIA shares have more than tripled, showing a 235% return this year, while AMD quadrupled to the tune of 304%.

Now, AMD pushed its PC and server chip releases into 2017, but Polaris is pulling its weight with confidence in the meantime. Both Polaris and Pascal have the potential to reach brand-new markets, as their number-crunching powers happen to be very useful for supercomputing tasks such as real-time artificial intelligence and high-speed data analysis.

Will these turnarounds reach even higher highs next year? You tell me. AMD and NVIDIA must continue to execute in order to reach higher, which is hardly a guaranteed outcome if you've been following these companies for a few years. In particular, AMD cannot afford to flub its next processor launch, because graphics products account for less than one-third of AMD's overall sales. This launch will make or break the bulk of AMD's revenue stream.

So I'm staying away from both AMD and Nvidia here because I'm not terribly convinced that the smooth sailing will continue. And even if you disagree with my assessment of the investment risks involved, it would be reckless to back up the truck at this point. Momentum plays can be great while they last but they cannot last forever, you know.

Surprise hit Stranger Things is helping Netflix gather and hold on to subscribers. Image source: Netflix.

Leaving obvious Netflix returns on the table

Okay, so why do I feel like I stiffed myself by not buying more Netflix this year? The stock is only trading sideways year to date.

For starters, the ever-volatile stock took some dramatic dives in February and July. The first drop provided as much as a 30% discount, and the summer swoon stopped at roughly 28%. Share prices have recovered strongly from these troughs, mostly thanks to a rock-solid earnings report in October. If you bought Netflix shares on Feb. 8, you'd be enjoying a 52% return on that investment today.

That's still less impressive than AMD's or NVIDIA's soaring jumps, I know. But the thing is, it was always obvious that these Netflix discounts would be temporary. They were negative reactions to positive news, opening obvious buy-in windows. I'm feeling silly for letting these opportunities pass me by.

In February, Netflix had just achieved nearly worldwide coverage with its streaming video services. That's paving the way toward massive revenue and profit growth in the long run, but at the cost of high short-term expenses. Result: lower share prices for all the wrong, downright myopic reasons.

Then, the company reported fourth-quarter results where pretty much every business metric came in ahead of management's guidance targets. But traders focused on the small miss on domestic subscriber additions, complained about the high costs of rolling out a global service, and punished the stock some more. Again, for all the wrong reasons.

The same issues festered for months, weighing heavily on Netflix shares for no good reason. Another turn in soft subscriber additions followed in July, as consumers turned their attention to election coverage and the Rio Olympics instead of to Netflix content: obviously a short-lived issue, with a near-certain rebound coming up ahead.

More missed opportunities.

The third-quarter report in October swept away many of the cobwebs, and Netflix shares broke loose to new all-time highs. Yes, a $46 billion market cap can grow 20% larger overnight.

No more deep-discount buying windows.

Yes, I wish I had dipped just a little deeper into the Netflix well at some point in 2016. There was really no reason not to, and several blindingly obvious chances to make a move.

Netflix already accounts for about one-third of my total nest egg, so I'll console myself with the fact that I'm spreading my eggs across several baskets instead. But Netflix remains the best investment idea on the table today, and looks likely to make a big positive move in 2017 as management is shifting its focus from expansion to turning a profit.

I'm not exactly missing out on that jump, but I could have taken an even bigger position at a fantastic buy-in price.

Oh, well. Always forward.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.