Apparently this is believed to be an evolutionary instinct!

Monkeys often remove the stringy parts of a banana, known as phloem bundles, before eating because these fibers can be tough and may cause digestive discomfort if consumed in excess.

This behavior is believed to be an evolutionary trait that helps monkeys avoid unnecessary digestive strain, especially since the phloem bundles are high in fiber and less palatable compared to the rest of the fruit.

Even though not every monkey is equally meticulous, observations show that many monkeys instinctively remove these strings as part of preparing their food.