I’m not sure I understand this. Small scale fluctuations are the easiest things to achieve, in fact they occur spontaneously. It’s the large scale fluctuations that would be difficult to achieve.

For example if you have a room filled with air, then changing the temperature of all the air in the room would require doing a lot of work or transferring a lot of heat to the entire room. But on the microscale, if you were to look at a random 1 micrometer cube volume of the air, then you should expect temperature fluctuations to occur all the time, even without the addition of heat or work to the room.

It’s like staring at static on a tv screen. The overall shade of the entire screen is middle gray and over time stays gray, but unsurprisingly individual pixels will fluctuate randomly between pure black and pure white. Small scale fluctuations occur spontaneously.

This is the truest shower thought I’ve ever seen