Positive Beats Negative

The Mitzva of Tzitzit has a unique aspect connected to it. There is a commandment not to wear a garment that has a mixture of wool and linen. This is called “Shatnez.”
This is why observant Jews have their suits checked for this forbidden mixture. Sometimes a suit might be 100% wool, but they might use linen padding in the collar or shoulders.

Despite this law, it is permitted to have wool fringes and a linen garment that make up a pair of kosher Tzitzit. The reason why it is permitted is based on a Halachic principle.

When you have a positive commandment (the obligation to wear Tzitzit) against a negative commandment (the prohibition to wear Shatnez), the positive commandment nullifies the negative commandment.

Another example of this principle is the prohibition of cutting off a leprous growth. However, if it happened that this leprous growth was on the foreskin of a baby, it may be cut as part of the ceremony of Brit Mila.

The positive commandment to circumcise a Jewish baby, cancels the prohibition of cutting a leprous growth.
Jewish Law is fascinating when one learns it in depth, and applies its various principles. It becomes obvious that such laws could only come from Hashem, Himself.