The first time I heard of the 30/20/50 theory I was just beginning my career in management. Over the past 10 years of my career I have adopted this theory as part of my personal management philosophy.
Here is how the equation breaks down: 30% of the people in your company are truly committed to their jobs and will always go the extra mile. These people have positive attitudes, rarely complain and typically advance the quickest and farthest in their careers. These are your "go to" people. 20% of the people in your company are the exact opposite. They are negative. Nothing is ever good enough for them and the company doesn't do enough for them. They are always complaining and usually the first to leave at the end of the day. 50% of the people in your company sit right in the middle. This group really just wants to get their job done and do what is expected of them.
The challenge for management is to stay focused on the 30% and not fall into the trap of trying to change the 20%. The danger is spending too much time with this group. Ultimately what happens is the 50% group begins to pay close attention to management's focus on the 20% and starts to think the 20% group must have some merit to their position. The 50% group now begins to behave in the same manner. This can lead to a net atmosphere of 80% of your workforce in the realm of negativity and your business is at risk. If this atmosphere is prolonged, you not only continue to put your business at risk but your top performers (30%) view their efforts as being taken for granted and may begin looking for a new company to work for.
The flip side to this is if you stay focused on your star performers, the 50% group will recognize management spending their time with the 30% and behave in a similar manner.
At this point you may be thinking to yourself the same thing I thought when I first heard this theory. That is, why not just get rid of the 20% and have the perfect team? Although there are exceptions to everything and this is possible, the theory holds that this equation always balances out. If you remove the 20% it is likely someone from the 50% may disagree with your decision. This may be the beginning of that person harboring their negative outlook on management's decision and over time they themselves move from the 50% group into the 20% group. Once this happens, they begin to recruit people to their side.
In closing I want to make sure I have not implied you should ignore the 20% group of your workforce. You should be fair and give their concerns consideration and make changes if they are warranted. The overall message here is to focus on what is working (and the people making it work for you) and not get caught up in others negativity.