"It's indeed surprising that replacing the elementary particle with a string leads to such a big change in things. I'm tempted to say that it has to do with the fuzziness it introduces"

This quote by Edward Witten is referring to the idea that changing a primary particle with a string can have a significant effect on the result of a situation. Witten suggests that this is due to the fuzziness that the string introduces. This could be referring to the reality that strings are more complicated than particles, and therefore can introduce more variables into a scenario. This could cause a much various result than if the particle was utilized instead. Witten is surprised by this, and is tempted to associate it to the fuzziness that the string introduces. This could be due to the fact that the string has the ability to engage with more variables than the particle, and therefore can lead to a much different result.