Those squares on the end of some area sidewalks aren't there to trip rollerbladers. They actually have a purpose that's extremely useful for some people.

I'll be honest, I had no idea what the pink colored bumpy panels on Sartell sidewalks were for. I know I didn't like them because they made it difficult to get on the sidewalk with rollerblades. They actually serve a purpose that is far more important than to annoy rollerbladers, they're for visually impaired or blind people.

Where the sidewalk ends and the road starts, the surfaces are even. For visually impaired people, it can be difficult knowing when they're no longer on the sidewalk, and that's a very dangerous scenario. The raised dots are at the end of the sidewalk to let those people know that the sidewalk ends and the road is ahead.

According to tiphero.com, the dots were introduced by Japan in the 1960's, and is considered "tactile paving". Some consider it as "sidewalk braille". There's different dot patterns and shapes for different scenarios. Each country can be a little different.

You'll generally see a dot pattern at the end of sidewalks, and pill-shaped dots around railways and subways. Here's a great video explaining all about sidewalk braille. Now that you know what they mean, you'll probably notice them everywhere!