A Suggestion for Long-Term Practitioners
For long-term zazen practitioners, the ego gradually becomes less prominent in their lives. Whether they put it into words or not, they have learned that the ego is not substantial or real, but merely an idea that they can put aside. I think I have learned this.

I have experienced, however, that the ego continues to make an appearance now and then and to cause unfavorable emotion or behavior. I can react angrily to something someone says or does. I can feel unaccountably sad and despondent.
I think that other long-term practitioners may have similar experiences, finding themselves slipping occasionally in their feeling and behavior. I have learned, however, that there is no point to being hard on myself because of such slips.
Ajahn Chah in Food for the Heart (Boston, 2002) expresses what I think I have seen myself. He says that after a spiritual seeker has seen or sensed the unreality of ego, nevertheless the ego may reappear, much like “a child who likes to play and frolic in ways that annoy us.” He continues,
We should understand that it’s natural for a child to act that
way. Then we can let go and leave them to play in their own
way. So our troubles are over. How are they over? Because
we accept the ways of children. Our outlook changes and we
accept the true nature of things. We let go and our heart
becomes more peaceful. (p. 157)
Of course if the child misbehaves frequently, there may be a need for self-control. Otherwise, if you slip, just accept it and forget it.