Nicholas Carlson explains:

Now, 18 months later, industry people are starting to believe that Systrom was wrong to accept that deal.

They believe that if Instagram had stayed an independent company, it could be worth between $5 billion and $15 billion today.

This morning, activist investor Eric Jackson tweeted: "Systrom has to be feeling like he totally missed this wave. Instagram likely worth $15B today minimum."

Jackson told us he came up with that valuation figure by looking at Instagram's total active users, about 150 million, and Twitter's, around 236 million. Assuming that Instagram's user-base is more US-weighted, and therefore more valuable, he figures Instagram's market cap as an independent company would be at least half of Twitter's $30 billion.

Startup investor Shervin Pishevar agrees that Systrom sold cheap. He wrote a tweet saying, "Instagram would be worth $5B+ today. It buttressed FB stock & gave it's mobile strategy legs. Insanely smart,cheap acquisition by Zuck."

Another group of people who believe that Systrom sold too soon are some of his former Instagram investors.

This morning, the New York Times's Jenna Wortham reported that venture capital firm Benchmark was "disappointed when Instagram’s founders decided to sell to Facebook for $1 billion last year."

Wortham writes, "Despite the high price tag, the firm thought Instagram could have succeeded as a stand-alone company, or at least could have brought a higher offer."

Wortham says this disappointment was a big reason why Benchmark pushed another startup it has invested in since, photo-sharing app Snapchat, to reject an all-cash $3 billion offer from Facebook.

So, did Systrom screw-up selling early?

Technically…yes. Instagram, if were an independent company today, would easily be worth 10X what it sold for back in 2012.

But no, Systrom did not screw up.

Mark Cuban once sold a company to Yahoo for stock. He sold the stock as soon as he was able. Then the stock went up some more. The next time he was on CNBC, an anchor asked him:  “Don’t you feel dumb that you cashed out your Yahoo (YHOO) stock at $200 and now it’s trading at over $230?”

Cuban's answer: “Well, it’s hard to feel dumb when you’re flying around in your G-5.”

He's got a point. This is a G-5:

I haven't heard anyone say Tumblr blew it selling to Yahoo for $1 billion.

So I'm going on record saying that Tumblr just like Instagram could have been worth much more.

Is it a risk to say such a thing? I doubt it.  

Go on the line now. PW is $1B value today!