The 1/4" end has 2 connections (signal, ground) & the XLR end has 3 connections (+ phase, - phase, ground). So how do 2 connections magically become 3? They don't.

Inside the XLR, pin 2 is connected to the 1/4" hot, but what about pin 3?

It usually gets tied to ground.

Why should you care?

Without all 3 pins, the connection is not balanced, meaning it can't reject radio interference. Essentially it's become a giant 1/4" to 1/4" cable. It's not the XLR connector that matters, it's the balanced audio behind it.

The signal is sent down 2 wires, pin 2 is the normal signal, but pin 3 is the out of phase. A mirror image of pin 2. Since radio interference would hit both wires, when you take the DIFFERENCE between pin 2 & 3 you get the signal, but the rf noise is gone. This is balanced audio, and it has to be XLR on BOTH ENDS.

What should you do instead?

This is what a direct box is for. 1/4" unbalanced in. Transformer inside balances the signal. XLR out with the ability to lift ground in case there's a buzz.