Whenever you feel content, look ahead. Lift your head out of the daze of contentment and look ahead to what is to come. If you have clear vision you will see something that brings you out of that daze.
The notion is not to become ego-crushed by this but to open yourself to discipline rather than depression. Catalyzing truth is healthier than deliriously content illusion.
This is not to say to never be happy, but that before we get to lasting happiness we will move through many layers of illusory contentment and this is just the forgetfulness of what inner work can be done.
Even then, once we find that lasting happiness, we may soon learn that this happiness, like all happiness is only temporary and true happiness is not from the superficial contentment we feel when we are physically, mentally and emotionally at rest, but when we are harmonized between all three fields of being and that way even in times of stress or work we can be happy and motivated to continue.