Inessential complexity increases the workload of maintaining a system (like the climbing wall vs. stairs: can't maintain an upstairs floor unless you maintain the ability to use the climbing wall).
Bells and whistles, especially when it comes to making things perfectly tidy, tend to introduce a lot of rules for using and maintaining a system. For example, a color-coding system with too many colors to reasonably recall without daily practice from using the system: any interruption, such as a vacation or even a weekend, will disrupt in some way the ability to use and maintain the color-coding system.
Informal rules also accumulate over time, adding to the complexity of any given action. It doesn't take a major change to topple your flashcard system, but slow, accumulated changes have been enough to do so.
Bells and whistles, especially when it comes to making things perfectly tidy, tend to introduce a lot of rules for using and maintaining a system. For example, a color-coding system with too many colors to reasonably recall without daily practice from using the system: any interruption, such as a vacation or even a weekend, will disrupt in some way the ability to use and maintain the color-coding system.
Informal rules also accumulate over time, adding to the complexity of any given action. It doesn't take a major change to topple your flashcard system, but slow, accumulated changes have been enough to do so.