yadyadaacharati shreshthastattadevetaro janaha |
sa yatpramaanam kurute lokastadanuvartate || 21 ||

Whatever an ideal person does, so do other people (imitate him). Whatever standard he sets, other people follow.

yat yat  : just as
aacharati : a person does
shreshthaha : ideal
tat tat : in that manner
eva : only
itarah : other
janaha : people
sah : he
yat : whatever
pramaanam : standard
kurute : does
lokah : other people
tat : like him
anuvartate : they behave

In the previous verse, Shri Krishna provided the example of king Janaka who, though being a warrior king, achieved self-realization through performance of karma yoga. Here Shri Krishna puts forth yet another argument to Arjuna, knowing very well that Arjuna always put others first before himself. Shri Krishna said that whosoever looked up to Arjuna as a role model would also take to this path if Arjuna followed it.

Now, an extremely important but subtle point made by Shri Krishna is hidden in the phrase “ideal person does”. He wants us to realize that actions speak louder than words. For instance, we cannot expect our children to not drink alcohol or smoke if we preach to them, but drink and smoke ourselves. Not just children, but most people watch what we do and not what we say. Therefore, Shri Krishna urges us to practice karmayoga, and not to simply tell people that we are learning it and so on.

So in addition to urging us and Arjuna to perform karmayoga, Shri Krishna also reveals an important leadership lesson. The best way to lead is to lead by example, and not by making flowery speeches or hiring motivational speakers. This point is not just echoed in the management texts of today, but also in spiritual masterpieces such as the Dasbodh by Samarth Ramdas Swami.