Not reading your sous vide instructions
This could be obvious, but it should still be mentioned. Read the directions carefully. Every sous vide is prepared uniquely and includes clear instructions to make the procedure simple. There are a ton of factors to take into account when choosing your water cooker, which means there are a ton of clear and subtle variations between each model that may make or break your finished product. Some sous vide appliances let you set the temperature for novices, while others allow you complete control. This is crucial to take into account since, if you think temperature control is automated, you may need to conduct further research before beginning.
The models' ability to be immersed into any bought pot or whether they come with their own water unit is another variation between them. The sum of all these minor variations can drastically change how you sous vide. Even if reading instructions is never enjoyable, doing this will ensure your success and satisfaction in the kitchen.