Spurs icon David Robinson might have retired in 2003, but that doesn't mean he's not keeping up with the NBA's comings and goings. So of course he's caught wind of the Golden State Warriors' signing of Kevin Durant this summer, but Robinson doesn't believe Golden State is going to be unbeatable for years to come.

Actually, Robinson thinks the Warriors' window with this superteam won't be as long as many expect and that judging from previous Big 3s, this won't be as easy as many believe it will be.

"It takes time, you look at what happened with LeBron (James), (Dwyane) Wade, and (Chris) Bosh. It took them a year or two to get their legs underneath them and figure things out and even then that run was relatively short," Robinson told Complex Sports.

More from FoxSports

The Heat did take a season before they won their first title after adding James and Bosh. But Miami's Big 3 made it to four consecutive Finals, winning two. That's not exactly a failure but far from the "not five, not six, not seven" that James so famously promised.

Robinson believes the Warriors will be hard-pressed to keep their four stars under contract long term, limiting this group's time together.

"So if you're able to put together a team like this, you're generally going to have a short window because you can't pay all those guys to keep them together," Robinson said. "There's the short window that's going to end relatively quickly and it's not as easy as going out to play."

Stephen Curry's contract ends next summer and he will be in line for a huge raise. He currently makes $11 million a year, a far cry from the max contract he will command in 2017. Durant's current deal will end in 2018 (though he can opt out to become a free agent after the 2017 season), Klay Thompson will be a free agent in 2019 and Draymond Green's deal is up in 2020.

Yes, the salary cap is expected to expand each year thanks to the TV contract, but unless the Warriors' Big Four is willing to take a bit of a pay cut, it will be difficult for Golden State to retain this group for the long term.