There is a Big Mind and a small mind. Sometimes the Big Mind wins over the small mind and sometimes it is the other way around.
When the small mind wins, it causes misery and when the Big Mind wins, it is joy. The small mind promises joy but leaves you empty-handed. You may initially be resistant to the Big Mind but it will fill you with joy.
The word guru means great. Jaya means victory. Deva means one who is fun-loving, playful, light. Some who are playful are often not dignified, and those who are dignified are often not playful. Jai Guru Dev means victory to the Big Mind in you that is both dignified and playful. Jai Guru Dev means “Victory to the greatness in you.” You do not say victory to the master as he has already achieved the Big Mind. You say victory to your own Self, your own Big Mind, which is being protested by the small mind.